The Complete Book on Gums and Stabilizers for Food Industry

Published: 2010Publisher: Asia Pacific Business Press Inc.
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Gums are plant flours (like starch or arrowroot) that make foods & other products thick. Gums are used in foods for many reasons besides being used as a thickener. Gums are important ingredient in producing food emulsifier, food additive, food thickener & other gum products. The main reason for adding a gum or hydrocolloid to a food product is to improve its overall quality. India is the largest producer of gums specially guar gum products. Similarly stabilizers are an indispensable substance in food items when added to the food items, they smoothens uniform nature and hold the flavouring compounds in dispersion. Gum technology stabilizers are carefully controlled blends of various food ingredients. Most processed foods need some sort of stabilization at some point during production, transportation, storage and serving. The science and technology of hydrocolloids used in food and related systems has seen many new developments and advances over recent years. The breadth and depth of knowledge of gums and stabilizers has increased tremendously over the last two decades, with researchers in industry and academia collaborating to accelerate the growth. Gums as food constituents or as food additives can influence processing conditions in the following ways; retention of water, reduction of evaporation rates, alteration of freezing rates, modification of ice crystal formation and participation in chemical reactions.
Some of the fundamentals of the book are functions of gum, typical food applications, gums in food suspensions, rheology and characters of gums, natural product exudates, flavor fixation, ice cream, ices and sherbets, gelation of low methoxyl pectin, seaweed extracts, microbial gums, transformation of collagen to gelatin, cellulose gums, dairy food applications, bakery product applications, analysis of hydrocolloids, gums in food products, general isolation of gums from foods, identification of gums in specific foods, group analysis and identification schemes, group identification methods, qualitative group analysis etc.
This book contains rheology of gums, plant sheet gums, microbial gums, cellulose gums and synthetic hydrocolloids different stabilizers used in food industry. The book will be very resourceful to all its readers, new entrepreneurs, scientist, food technologist, food industries etc.

Sample Chapters

Functions of Gum

An
army marches on its stomach is
an old expression, widely attributed to Napoleon. It is unfortunate,
but true,
that many advances in technology have been greatly accelerated and
expedited by
the contingencies of war. The need for preserving foods for long
periods of
time during the Napoleonic campaigns led directly to the development of
the
canning process by Nicholas Appert in 1810. Considering the state of
science
and general lack of information at that time, this ranked as a
considerable
achievement.

A century
later
with the proliferation of little wars that eventually culminated in the
First
and Second World Wars, the logistics of supplying food for armies
scattered
over the world, led to many other advances in food science. Marked
progress was
made in the preservation of foods by quick freezing, irradiation,
chemical
additives, dehydration, and other methods.

Developments
in
dehydration technology were spurred by the need for transporting foods
long
distances by ship or plane. It is a rare soldier that does not recall
with
nostalgia perhaps, but not regret the powdered eggs and dehydrated
potatoes
that were part of the daily rations of the American soldier overseas
during
World War II. It is encouraging to report that these products were
vastly
improved during the years after the war, and today they can be
considered to be
quality products of the convenience food type.

Convenience Foods

The concept
of
convenience foods with the built in maid ushered in a period of great
innovation
and technological advances in the food industry. This era, which also
started
during World War II, was primarily a result of the great changes, which
took
place in the American home at that time. Many women, employed in war
industries, had limited time for the every day kitchen tasks, and were
ready
for any time saving devices and foods that might be offered. After the
war this
feeling of emancipation from the kitchen remained and became a way of
life,
which exists today.

Pioneers in
the
food industry were quick to perceive this trend and took advantage of
this
beckoning market by plunging into the development of all types of
convenience
foods. For a period of time it might be said that the prevailing
philosophy was
that of the famous gastronome Brillat Savarin when he made the
statement, which
appears, at the beginning of this chapter.

Instant Coffee

One of the
most
successful post war developments is that of instant coffee. Although
soluble
coffee was known before the war, it was not a widely accepted commodity
it varied in
quality, had poor stability, did
not dissolve too well, and was expensive. In short, it did not enjoy
popular
consumer acceptance. War time needs, being the mother of inventions,
led to
technological improvements in the development of good quality soluble
coffees
to be included in military rations. These products had good
performance,
stability, and taste characteristics as a result of drying the coffee
with
fillers such as sugar or dextrose.

A major
breakthrough was achieved subsequently with the development of a spray
drying
process for a 100% coffee product that had good flavor, performance,
and
stability. This 100% flavor bud product met with great success and
paved the
way for many similar products, resulting in continuous market growth
over the
past two decades. Today, instant coffee is so well entrenched in the
American
market, that it now outsells regular ground coffee. It has also been
predicted
that the current generation of teen agers who grew up on soluble coffee
will
become an adult market with a preference for soluble rather than
regular
coffee. This, of course, is conjecture and only time will tell.

Frozen Foods

The concept
of
quick freezing foods as a preferred method of preservation was
originally
developed by Clarence Birdseye in 1925. Applications of his methods led
to a
host of food products that could be processed in season and preserved
at the
height of their flavor and textural development until ready to use. No
longer
does the housewife have to screen the sand from her spinach, or remove
the
discolored and damaged leaves, or even core the vegetable. It is not
even
necessary to cook it, watching carefully until the vegetable is soft
and
tender, but not too soft and crumbly. Now all she has to do is remove a
frozen
package of cleaned, cooked spinach from her freezer, put it in a pot of
boiling
water, and heat it until thawed.

The
convenience
and high quality of frozen vegetables, fruits, meats, etc., met with
great
consumer acceptance in the period after World War II and resulted in
many new
products, the outstanding example of which is frozen orange juice
concentrate.

Freeze Dried Foods

The
subsequent
processing combination of quick freezing followed by low temperature
vacuum
dehydration was the logical outcome of a series of technological
advances. Many
new freeze dried food products have been developed, the most recent of
which
have been dry breakfast cereal combinations with freeze dried
strawberries,
bananas, and other fruits. Upon the addition of milk, the fruits
hydrate to
form truly fresh high quality fruits.

Gum Constituents

At this
point,
the reader might rightly ask, What does all this have to do with gums?
The
answer is, Everything. Gum constituents are present in almost every
natural
food and are largely responsible for the structure and textural
properties of
the plant. In prepared foods, gums are used as food additives to impart
desirable textural and functional properties to the finished products.
It is
rare that a convenience food does not have one or more gums listed
among the
ingredients. Gums are so necessary in many foods covered that they are
included
in these standards and are not required to be listed on the label.

The use of
gums
to obtain superior quality in many products has become so accepted in
certain
foods that it is difficult to find a sample without it, even if one
were to
want it. This is best illustrated by ice cream. In the good old times,
home made
ice cream like mother used to make suffered from poor textural
qualities such
as presence of ice crystals, sandiness, and lack of smooth melt down.
Today,
commercially prepared ice creams contain various hydrocolloids as
emulsifiers
and stabilizers to eliminate such defects of quality. It is almost
impossible
to find a brand of ice cream that does not contain gums.

Effect on Processing

All food
processes inherently involve the modification or denaturation of the
characteristic food texture. The properties of the gum constituents
present in
many food materials have an important bearing on processing conditions
and the
resultant properties of the final food product.

In almost
all
food processing there is a change in the moisture content or the
physical shape
of water. The water is either completely or partially removed, as in
dehydrated
foods or it is
physically changed to gas
in cooking and blanching operations or
it is converted to the solid form of ice in freezing operations. The
change in
the water content or its physical form is largely responsible for
changes in
texture of the processed food product, and is one of the most important
factors
to be considered in manufacturing high quality processed foods. Since
both
residual gum constituents and hydrocolloid additives greatly influence
the type
of physical transformation and rate of migration of the water
component, these
substances are important factors in food processing.

Pertinent Processing Parameters

Gums as
food
constituents or as food additives can influence processing conditions
in the
following ways: (1) retention of water (2)
reduction of evaporation rates (3)
alteration of freezing rates (4)
modification of ice crystal formation (5)
participation in chemical reactions. These
functional effects are not isolated phenomena, which can be followed
easily they are
only evident in the textural
qualities or rheological behaviour of the final product. While the
functional
effects of a gum are its most important characteristics in determining
its use
in foods, these effects must be considered in context with many other
factors,
including price, availability, ease of handling, and legal restrictions
related
to their use.

Function in Food Applications

Gums are
used in
a wide range of specific food applications, ranging from adhesives to
whipping
agents. Typical specific functions and food applications are shown in
Table 1,
but the general function of gums can be limited to their two major
properties gelling
and thickening.

All gums,
or
hydrocolloids, by definition and usage have a thickening, or viscosity
producing,
effect when dispersed in a water medium. This property is the basis for
their
use as bodying, stabilizing, and emulsifying agents in many foods. A
comparatively few of the important gums i.e., agar, algin, carrageenan,
furcellaran, gelatin, pectin, and starch also have the ability to form
gels
under specific conditions of use. Gels, when referring to foods, are
products
that will retain their shape and will not flow unless pressure is
applied.
Probably the most common gelled food product is gelatin dessert gel,
which has
enjoyed enormous popularity in this country for many years. Other well
known
food gels are starch based milk puddings, gelatin aspics, and pectin
gelled
cranberry sauce. In Europe, milk puddings of the blanc mange type are
very
pupular and are usually made with seaweed extracts of the carrageenan
or
alginate type.

There is an
interplay between the viscosity and gelling characteristics of any
specific gum
and these factors must be taken into consideration when these gums are
used for example,
depending on the type of gelatin
and on its concentration, gelatin can be used as a thickening agent
rather than
a gelling medium. In a related way, temperature also plays an effect as the temperature
increases, the viscosity
decreases, thus decreasing the effective thickening properties of the
gum. This
temperature increase is in most cases the same as an effective
reduction in gum
concentration.

Viscosity

Definition and Meaning

Viscosity
is the
resistance to flow of a liquid system. In colloidal suspensions it is
increased
by the thickening of the liquid phase as a result of liquid absorption
and
consequent swelling of the dispersed colloid. This thickening, or
viscosity producing,
effect of gums in food products is, in turn, responsible for other
functional
effects such as the suspension of solid particles, the emulsification
of oil
and water phases, the stabilization of liquid solid gas phases, the
dispersion
of solid and liquid phases, and related phenomena.

When
hydrocolloids are used as viscosity producing agents for the purpose of
suspending, emulsifying, or stabilizing a food system, shelf stability
is
extremely important and the selection of the proper hydrocolloid is
critical.
Degradation of the hydrocolloid and the resulting reduction in the
viscosity of
polymer solutions may impair the flow properties and appearance of the
product
sufficiently to reduce its consumer acceptability.

Since most
gums
are long chain polymers, they are subject to the type of molecular
breakdown
caused by cleavage of molecular bonds, resulting in lower viscosities.
Determination of the exact causes of degradation or loss of viscosity
is often
difficult. Frequently, polymers are degraded by the use of high
shearing
equipment used to put them into solution, or by the high temperatures
used in
processing. In general, the low viscosity natural gums are more stable
than the
high viscosity types. Studies on the comparative stabilities of gums
are more
valid if comparisons are made between solutions of equal viscosity
rather than
of equal concentrations, which is so often the case.

Factors Effecting Hydrophilic Viscosities

The
viscosities
of hydrocolloid systems are effected by many factors and listed ten
factors
that cause variations in the viscosities of hydrophilic systems: (1)
concentration, (2) temperature, (3) degree of dispersion, (4)
solvation, (5)
electrical charge, (6) previous thermal treatment, (7) previous
mechanical
treatment, (8) presence or absence of other lyophilic colloids, (9) age
of the
lyophilic sol, (10) presence of both electrolytes and nonelectrolytes.
The
importance of viscosity to the textural quality and consistency of most
foods
is so great that above factors to be the ten commandments of food
preparation.
She illustrated the importance of some of these in the preparation of a
simple
custard dessert: concentration of egg or protein micelles temperature of cooking degree of dispersion of the
micelles degree of
hydration which is influenced by the
type of reaction and presence of salts beating
of the egg use of
milk or water aging
of the custard as well as the age of the
eggs and milk presence
of electrolytes
in egg and milk and addition of salt presence
of nonelectrolyte, sugar. The
viscosity of any food system is subject to the influence of many
complex
parameters, and the hydrocolloids present or added are likewise subject
to the
same forces encountered in the preparation of quality food products.

Typical Food Applications

The use of
gums
solely for thickening purposes is common in such products as pie
fillings and
beverage dry mixes. In pie fillings, especially fruit type fillings,
gums are
used to thicken the fruit juice to prevent the flow of the filling from
the pie
shell. In beverage mixes that are reconstituted with water, gums are
used as
thickening agents to give the final product the necessary body. This is
especially true for the sugar free, dietetic products.

Soups and
soup
mixes are thickened with starches and gums to improve their body and
consistency. Likewise, sauces and sauce mixes contain gums to impart
desirable
texture and flow characteristics. For low pH sauces, it is necessary to
select
thickening agents that are resistant to acid degradation. Gum
tragacanth and
propylene glycol alginate are two of the preferred additives, since
they are
more acid stable than the other common gums.

Thickening
agents are incorporated into many breading mixes, so that they will not
run off
meats and fish. Gums have also found a novel use in dog foods where
they are
added to dry meatlike pieces, which, upon the addition of water,
hydrate and
thicken to form a thick gravy like sauce containing meatlike chunks.

Gelation

Hydrocolloid
food gels are rigid, two phase systems that show resistance to flow
under
pressure and are capable of retaining a firm, distinct structural form.
They
are liquid solid systems with a continuous network of solid material
forming
the gel matrix and enmeshing or holding a continuous or finely
dispersed liquid
phase. The solid, backbone phase is usually composed of long chain
molecules in
the form of a mass of intertwined fibrils linked by primary or
secondary bonds
at widely separated sites along the molecule.

Although
gels
can be considered primarily to be solids, they exhibit properties of
both
solids and liquids. They resemble solids in their structural rigidity
and
elastic response when distorting forces are applied, and they resemble
liquids
in their vapor pressure, compressibility, and electrical conductivity.

Mechanism of Gel Formation

The
beginning of
gelation is shown initially by the gradual decrease in Brownian
movement of the
colloidal particles concluded within the gel. This decrease is caused
by the
exertion of long range forces between the molecules, which in turn
results in
the hydration and coherence of the particles. The viscosity then begins
to
increase as gelation proceeds and the solvent (liquid) is absorbed by
the
swelling solute (solid) and is gradually immobilized. As the process
continues
a three dimensional network containing enmeshed portions of the liquid
is
gradually built up. The various fragments of the gelling polymer
continue to
react and finally form one large continuous structure. At this stage
the
rigidity of the system becomes apparent. Parts of the large molecular
chains in
the network can still react with other parts by cross linking to
further
increase the rigidity of the whole structure.

Gelation from Sol State

Gelation
can be
induced in both sol or solid state systems. From the sol state,
gelation can be
achieved by increasing or establishing forces between solute molecules
in one
or more of the following ways: addition of a nonsolvent evaporation of the solvent
present in the
system addition of
a cross linking agent
reducing the
solubility of the solute by
chemical reaction changing
the
temperature adjusting
the pH.

Gelation from Solid State

From the
solid
state, gels can be formed by allowing the solid phase to remain
immersed in the
solvent until sufficient liquid is imbibed to form a gel. Thus, a gel
can be
considered to be in an intermediate state of hydration between a sol
and a
solid.

Types of Gel Linkages

The
formation of
gels from solutions of long chain polymers can be explained as being
due to the
cross linking of adjacent molecules to form a continuous network
possessing
mechanical stability in the final gelled state. Entrapped within this
network
is a continuous liquid phase consisting of the solvent and solutes,
some of
which may include non cross linked polymeric materials.

The types
of
cross linking that may take place depend on the chemical properties of
the
constituent groupings on the polymers forming the gel matrix and the
chemical
conditions existing in the system.

Rheology and Characters of Gums

The main reason for adding a
gum or hydrocolloid to
a food product is to improve its overall quality. This improvement may
relate
to its appearance, convenience, stability, cost, texture, etc., all of
which
are eventually judged by the consumer. The consumer usually judges the
product
by simply eating it and seeing how it tastes. At this point he does not
care if
the added gum is a galactomannan or a sulfated galactan, nor does he
worry
about whether the vitamin A in the product is naturally derived from
sharks
liver or synthesized from b ionone. He is concerned with the taste and
mouth
feel of the product. If it tastes good, he is happy
if
it tastes bad, he is unhappy, and so
eventually is the manufacturer of that specific food item.

Consumer
acceptability the
objective of every company selling food is directly related to food
texture and
flavor. At the risk of oversimplifying, it can be assumed that these
two
factors, texture and flavor, are the two most important properties of a
food
comestible, although it is conceded that other factors such as
appearance,
color, packaging, convenience, price, calorie content, etc., are also
important
and often supersede texture and flavor. But for mass market acceptance,
good
flavor and texture are essential. With products such as soluble coffee
and
frozen orange juice concentrates, the flavor characteristics alone have
been
sufficient to separate the products of good quality from the inferior
brands.
In the case of ice cream, the textural qualities predominate and serve
to
distinguish the good from the bad. Poor quality ice creams may have a
gritty
consistency due to ice crystal formation, while good quality ice creams
are
uniform and have a homogeneous texture leading to smooth melt down in
the
mouth. It is obvious that no one would buy a product that had a poor
flavor or
texture at least
not the second time.

Oldfield makes the point that
foods that cease to
yield flavor before they have been sufficiently chewed for comfortable
swallowing tend to produce an aversion towards further chewing together
with an
involuntary inhibition of the swallowing mechanism. He illustrates this
with
the impulse to spit out over cooked, tough steak. Another common
example is
that afforded by chewing gum. Most people will chew gum until the
flavor is
leached out and will then discard it even though the textural and
chewing qualities
have not been impaired.

While
flavor is
somewhat influenced by gums, in that gums play a part in flavor release
and
flavor retention in foods and are used to stabilize and fix flavor
emulsions,
the most important effect of gums is on texture. Texture is an abstract
concept
of a concrete property. All foods have texture if we think of texture
as being
the structural matrix of the food, but it is the perception of texture
when the
food is eaten that is important. This was most clearly stated by
Szczesniak who
defined texture as the composite of the structural elements of the food
and the
manner in which it registers with physiological senses. The importance
of the
physiological stimuli during eating is best described by Oldfield. Once
biting
and chewing start, an immensely complex pattern of stimulation is set
up. With
the help of the tongue the food is rolled across the gums and the hard
and soft
palates. The teeth themselves play a part in signalling the textural
and
rheological properties of the food and
these properties are progressively changed by the process of
mastication, while
a changing pattern of stimuli results. As the food is broken up by the
teeth,
the increased surface area releases taste and smell stimulus substances
in
greater quantity. All these stimulus elements contribute to supply the
brain
with the material out of which it constructs the complex perception,
and they
also serve, some without entering consciousness, to maintain and modify
the
activity of the mouth. Eventually the food is swallowed.

Thus the
act of
eating (i.e., chewing and swallowing) can be visualized as a process of
breaking down (or deforming) the food product in the mouth, with the
type or
character of the breakdown being dependent on the structure or texture
of the
food. In recent years this important area of investigation has been
formalized
into a branch of science known as rheology, the science of the
deformation and
flow of matter.

While it is
not
the purpose of this chapter to delve deeply into the subject of
rheology, a
subject, which is still regarded by some as a messy science, it is
important to
be able to understand the methods and instruments of rheology in order
to
measure and explain the effects of hydro colloids on food textures. Any
tool that
gives a meaningful number to a textural parameter, which in turn can be
related
to consumer acceptability, is useful to the food scientist. The phrase
meaningful
number must be carefully qualified, because many numbers are not
meaningful and
bear no relationship to the textural acceptance of the product in
question.
Thus the viscosity of beverages is not necessarily correlated with the
mouthfeel or acceptability of the beverage. Beverages of identical
viscosity
can be either slimy and mouthcoating or smooth and pleasant. Likewise
gel
strength measurements on standard instruments such as the Bloom
gelometer, will
give satisfactory data on the overall strength and rigidity of the
gels, but
will completely fail to characterize the parameters of elasticity and
brittleness which may be more important from the viewpoint of consumer
acceptance.

Certain
measurements, however, can be objectively correlated with mouthfeel and
consumer approval. Recent work established a correlation between the
organoleptic characteristics of hydrocolloid solutions and their
rheological
behavior. Measurements of solution viscosities at various rates of
shear showed
a relationship between the shape of the curve and degree of sliminess.
This was
subsequently confirmed in work on gum thickened sucrose solutions.

Studies of
various hydrocolloid solutions showed that they could be grouped into
three
categories slimy, slightly slimy, and nonslimy–depending upon the shape
of the
curve (Fig. 1). This was a practical way of measuring rheological
parameters of
gums and using the physical data to select the ones preferred with
respect to
mouthfeel or texture.

The
rheological
behaviour of hydrocolloids is of special importance when they are used
in
artificially sweetened foods where large amounts of sugars are replaced
by gums
for bodying and textural effects. The organoleptic properties and
acceptability
of such foods are more critically related to their rheological
parameters than
sugarbased foods.

Thus, in
general, the overall objective in studying the rheology of food
products is to
measure the various parameters of foods under stress and to define them
mathematically so that they can be related to the subjective,
organoleptic
textural properties of the food.

Background

Although
the
word rheology is only about 40 years old, the science and practice of
rheology
goes back many centuries. The first known rheologist, Amenemhet, an
Egyptian
who lived about 1540 B.C., studied the effects of temperature on the
viscosity
of water and then described his observations in hieroglyphics. This
unlauded
scientist invented a clock, which consisted of a conical vessel from
which
water could be made to flow steadily. Time was measured as the height
of the
water remaining in the funnel. The angle of the cone puzzled modern
scientists
because it was not corrected to provide a fall in height proportional
to time.
However, when a replica of the clock was built and operated through the
great
temperature differences which exist between Egyptian days and nights,
the instrument
constructed by Amenemhet was found to be correct. Cold water has a
greater
viscosity, or resistance to flow, than warm water
the
angle of the cone had thus been calculated
and constructed to allow for this difference as the water was cooled by
the
cold Egyptian night.

In another
part
of the world, the Indians developed a crude system of rheology in about
100
A.D. which classified different substances into groups according to the
sense
responses of feel, temperature, sound, taste, and odor.

It wasnt
until
the sixteenth century, though, that any real progress in rheology was
made. At
this time, Leonardo da Vinci investigated the flow of water through
orifices
and channels, a series of experiments, which was followed in the next
century
by Galileos studies on the cohesion of ropes. Hooke subsequently
reported on
the elastic properties of solids and stated that stress is proportional
to
strain in elastic solids. Newton, in the same era, made the first
rotational
viscometer in the course of his studies of the rotation of the planets
in the
solar system. He used a rotating cylinder in a pool of water and
observed that
resistance to flow is proportional to the rate of shear in liquids.
This type
of ideal relationship was later termed Newtonian flow in honor of its
discoverer.

In the
nineteenth century, Poiseuille studied the flow of water through glass
capillary tubes and found that the quantity of water flowing through
such tubes
increased directly with the fourth power of the diameter of the tube
and directly
with the pressure of the water. In addition, the quantity of water
decreased
with increased viscosity and with the length of the tube. For his work,
Poiseuille was honored by having the basic unit of viscosity, the
poise, named
after him.

The father
of
modern rheology is considered to be Eugene C. Bingham who coined the
word
rheology from the Greek rheos meaning flow. His classic book, Fluidity
and
Plasticity established a firm basis for this new science. Later, like
so many
other scientific endeavors, the study of the rheology of polymers was
accelerated by the contingencies of war. For example, gasoline
thickened by
aluminum stearates used in flame throwers during the Second World War
showed
marked elasticity and peculiar flow properties. Rheological studies
were made
in an effort to understand and to improve the cohesiveness of the
thickened
ejected fuels. The flow peculiarities were attributed to normal
stresses, which
were pressures acting across or normal to the shear planes. After the
war, the
study of rheology led to the development of many useful products such
as
plastics, paints, foods, drugs, etc., and proved to be helpful in
advancing the
technologies of all of these industries.

Definitions

Rheology is
the
science of the deformation and flow of matter. It includes the study of
elastic
deformation and other phenomena not necessarily associated with flow.
Matter is
deformed, or starts to flow, only when it is acted upon by force. The
force may
be supplied deliberately, accidently, or may be all pervading as in the
case of
gravity. Rheology is concerned with forces, deformations, and time, and
may
also include temperature and other secondary parameters.

Food
texture is
a complex property comprising several interrelated physical parameters,
of
which viscosity in liquids and elasticity in solids are among the most
important. Other related properties are tackiness, smoothness,
plasticity,
particle size, density, and temperature. Most foods do not have simple
invariant rheological properties such as viscosities and elastic
moduli, which
are independent of stress and strain conditions and which can be
defined by a
single number. But the behaviour of these materials, even when they are
variable, can be expressed according to defined rheological
measurements and
must be represented by flow curves (rheograms) rather than single
numbers.

For a more
complete description of the rheological behaviour of fluid foods, Charm
believes that the parameter of tensile strength must also be considered
along
with shear strength and viscosity measurements. This property, although
rarely
measured, may play an important role in textural qualities and coating
behavior
of fluid foods. Charm measured the tensile strengths of catsup, tomato
paste,
and mayonnaise, and found them to be about twice the value of the shear
strength. The overall significance of tensile strength has not yet been
established, but it may be an important factor in defining the complete
rheological picture of specific food products.

The
prototype of
the perfect, or ideal, (Newtonian) liquid is one that flows at a steady
rate at
constant pressure and at a rate strictly proportional to each pressure
if a
series of pressures is applied. Other liquids whose rates of flow are
not
proportional to the pressure applied are called non Newtonian liquids.
With
respect to solids, elasticity and plasticity are two of the more
important
attributes of their structures.

Bingham
defined these properties
quite clearly. When a shearing stress is applied to a perfectly elastic
solid,
a certain strain is developed which disappears completely when the
stress is
removed. The process is reversible and no work is done. Likewise,
viscosity can
play no part in the movement. This is a classic case of elastic
deformation and
not of flow.

The
prototype of
the ideal elastic solid is based on Hookes Law and must meet the
following
criteria: (1) the deformation must be proportional to the applied force
(2) it must be
completely recovered when the
force is removed (3)
both the original
deformation and its recovery must not be delayed by internal
viscosities.

If a
shearing
stress is applied to a body that is imperfectly elastic, it will be
found that
at least a part of the deformation will remain long after the stress is
removed. In this situation, work has been done in overcoming some kind
of
internal friction. Plasticity can therefore be defined as a property of
solids
by virtue of which they hold their shape permanently under the action
of small
shearing stresses but are readily deformed, worked, or molded, under
somewhat
larger stresses.

The line of
demarcation between a liquid and a solid is sometimes very thin and
often
difficult to define, let alone, measure but
various situations will be reviewed in the
discussions of the different types of flow behavior found in food
products.

Viscosity

The most
common
way of characterizing a liquid or fluid material is by measurement of
its
viscosity, which is actually a measure of fluid friction. The force of
friction
can be considered as the energy required to move an object that rubs on
another, i.e., viscosity is the measure of the internal friction
resisting the
movement of each layer of fluid as it, moves past an adjacent layer of
fluid. A
highly viscous material is one possessing a great deal of internal
friction it will
not pour or spread as easily as a
material of lesser viscosity.

In
Newtonian
systems, where the shearing stress is directly proportional to the rate
of
shear, the viscosity is constant and a single point viscosity
measurement is
sufficient to characterize the system. It is only necessary to plot the
single
point measurement and draw a straight line to the origin to indicate
the true
flow curve.

However
most
fluid foods are non Newtonian systems where the viscosities are not
constant
but are dependent on the rate of shear. In addition, yield values and
the rate
of change in resistance to flow with increased shear are also needed in
order
to define the flow picture of some systems accurately.

The rate of
change in resistance to flow is a measure of the magnitude of the
systems non Newtonian
behaviour and can be ascribed to various factors such as: (1) the ease
of
alignment of long chain molecules in solutions
(2)
the nature and uniformity of the particle
size of the ingredients in dispersions or suspensions
(3)
the way the particles pack together in the
dispersion (4) the
amount of dispersion
liquid and the extent of voids created when the system is disturbed.

It is
easily
seen, therefore, that single point measurements with any type of
viscometer are
limited in meaning because they do not describe the flow behaviours at
varying
rates of shear and thus cannot adequately characterize the physical
structure
of the liquid.

Therefore,
depending upon their behaviour under imposed shearing forces, materials
are
categorized as Newtonian or non Newtonian. Only a few of these systems
are
present in food products, the more important ones being those where the
flow is
independent of time. These consist of Newtonian, Bingham plastic,
pseudoplastic,
and dilatant systems. Two other systems often encountered are
thixotropic and
rheopectic materials in which the flow is dependent on time.

Newtonian Flow

Newtonian
flow
can best be described by considering two parallel plates, A and B, of 1
cm2 area
(A), with the intervening 1 cm space being filled with the liquid under
consideration (Fig. 2).

Viscosity
is
equal to the force (F) that is required to induce a unit rate of shear.
The
depth (d) of the substance in between is 1 cm. If a force (F) of 1 dyne
is
required to move plate A with constant speed of 1 cm per second, then
the
viscosity of this substance will be 1 poise. The innumerable parallel
layers of
the substance must move past each other once plate A is moved.

If plate A
is
moved to the right, the layer next to the stationery plate B remains
without
moving. The layers above it travel, depending upon the distance from
plate A,
with an increasing speed to the right. Each single layer of the
substance,
therefore, passes the one below it and remains a little behind the one
above
it. Because the layers adhere to each other, a force is encountered
that
opposes this sidewise movement. This tenacity is called viscosity (h),
or
internal friction, of a system which, per unit area, is the same on
each layer.
Viscosity, then, is a measurement of the combined effect of adhesion
and
cohesion. The transmitted force (F) is therefore proportional to the
coefficient of the inner friction as follows:

The
(dv/dr), or
D, is the rate of shear and is directly proportional to the applied
force (F),
and flow starts under the slightest pressure. The characteristic flow
line of a
Newtonian substance goes through the origin of a plot (or rheogram) of
D versus
F.

Newtonian
fluids
exhibit direct proportionality between shear stress (F) and shear rate
(D). At
any given temperature, these materials have a viscosity that is
independent of
the rate of shear. In simple terms, it will take twice as much force to
move
the liquid twice as fast. As shown in Fig. 3, the relationship between
shear
force and rate of shear is a straight line and the viscosity, in
absolute
units, is the inverse slope of the line. The viscosity of Newtonian
liquids
remains constant as the rate is changed.

Newtonian
behaviour has been found to be common to all gases and to all liquids
or
solutions of low molecular weights i.e., non polymeric materials and
also to
solutions of low concentrations of some high molecular weight polymers.
The
common denominator of these solutions is that the dissipation of
viscous energy
in them is due to the collision of fairly small molecular species.
Newtonian
foods include most simple solutions, such as sugar syrups, broths,
bouillon
soups, soft drinks, and milk. Most foods, however, fall into the non
Newtonian
categories.

Natural Product Exudates

Origin of Gums

A great
many
plants exude viscous, gummy liquids, which when exposed to air and
allowed to
dry, form clear, glassy masses. The shapes of these masses vary from
spherical,
teardrop balls typical of gum arabic producing Acacia trees to curved,
ribbon like
strands of tragacanth from Astragalus bushes. The colors of these
exudates also
vary widely from almost clear white to dark brown, depending on the
species,
climate, soil, and absorbed impurities.

The basis
and
reason for the formation and exudation of gums by plants, is still not
understood, and many theories have been formulated to explain these
phenomena.
One theory suggests that gum formation is a protective mechanism
resulting from
a pathological condition. This hypothesis is supported by evidence
concerning
the production of gum arabic. Healthy Acacia trees, grown under
favorable
conditions of soil and climate, produce little or no gum, while trees
grown
under adverse conditions of high elevation, excessive heat, and
scarcity of
moisture produce sizeable quantities of gum arabic. And the yield of
gum can be
further increased by deliberately injuring the tree by stripping away
the bark.

Other
investigators believe that gum formation is part of the normal
physiological metabolism
of the plant as in the case of the gums in sugar beets and yeasts.
Still others
consider gums to be synthesized as a result of an infection of the
plant by
microorganisms in an effort to seal off the infected section of the
plant and
prevent further invasion of the tissue. This would probably be similar
to the
formation of a scab on a human wound. The formation of gum has also
been
attributed to fungi attacking the plant and releasing enzymes that
penetrate
the tissues and transform the constituent cellulose materials of the
cell wall
into gum. This has been suggested to be the mechanism of formation of
the gum
found in the gummosis disease of various deciduous trees. Yet another
theory,
particularly with respect to Acacia species, claims the formation of
gums to be
caused by bacterial action and suggests that specific bacteria are
capable of
producing different kinds of gum.

The most
reasonable explanation however, seems to be the simplest one, namely
that the
plant produces the gum in order to seal off the injured part, primarily
to
prevent the loss of moisture and not necessarily to prevent infection.
This
concept is supported by the fact that gum arabic and gum tragacanth are
both
produced immediately by healthy trees that have been deliberately
injured. But
whatever the cause, it is fortuitous that many species of plant produce
large
quantities of gums that can be utilized in a constructive manner.

Physical Properties

The
physical
appearance and properties of the natural gums are of utmost importance
in
determining their commercial value and their end use. These vary
considerably
with gums of different botanical sources, and there are even
substantial
differences in gum from the same species when collected from plants
growing
under different climatic conditions or even collected from the same
plant at
different seasons of the year. The physical properties may also be
affected by
the age of the exudate, treatment of the gum after collection, such as
washing,
drying, sun bleaching, and storage temperatures.

Natural
gums are
exuded in a variety of shapes and forms, the best known being the
teardrop or
globular shape of various grades of gum arabic. Other characteristic
shapes are
flakes or thread like ribbons as with gum tragacanth. Still others
resemble
stalactites and after collection and fracturing yield irregular rod
shaped
fragments.

The surface
of
most gums is perfectly smooth when fresh but may become rough or
covered with
small cracks or striations upon weathering, resulting in an opaque
appearance.
These fissures or striations are often restricted to the surface, but
may be
deep in some gums, causing the tear drops to break up into smaller
fragments
during handling and shipping.

The color
of
gums in their natural exudate shape varies from almost water white
(colorless)
through shades of yellow, amber, and orange, to dark brown. The best
grades of
gum arabic are almost colorless with slight traces of yellow. Some gums
possess
pink, red, or green lines and
some black
or brownish gums are also found.

Many gums
when
first secreted appear to be colorless, and it is believed that color is
due
mainly to the presence of various types of impurities. Color often
appears as
the gum ages upon the tree and may be due to extraneous substances that
are
washed onto the gum. Bush or grass fires can cause discoloration by
scorching.
Tannins from the sap or tissues of the parent tree are frequently the
cause of
discoloration and are believed to account for some of the very dark
gums
yielded by certain trees.

The water
soluble
plant gums are usually odorless and in this respect differ markedly
from the
oil soluble resinous exudates which have distinctive smells. The gums
are
usually tasteless and bland, except for some species which have a
sweet,
carbohydrate taste and some types that have been contaminated. Gums
contaminated with tannins usually have a harsh, bitter flavor that is a
serious
disadvantage in food applications.

Gums vary
in
hardness, but since this is usually dependent upon the amount of
moisture
present (12 16%), it cannot be used as a means of classification as
with
minerals. Density is also variable and depends upon the amount of air
entrapped
when the gum was formed.

There are
many
plant gum exudates known all over the world, but only four are of real
importance to the food industry. Many of the other gums are known and
used in
local areas where they are available, but only to a very limited
extent. These
gums have similar properties and can be used for similar applications
where
necessary. Some of the more common ones are damson, plum, cherry,
peach, prune,
lemon, almond, cashew, brea, chagual, mesquite, shiraz, cactus, neem,
sapote,
cholla, khaya, jeol, and many more too numerous to mention.

Gum Arabic

The oldest
and
best known of all natural gums is gum arabic, also known as gum acacia,
Turkey
gum, gum Senegal, and by many other descriptive and colorful local
names. Gum
arabic is the dried, gummy exudation obtained from various species of
Acacia
trees of the Leguminosae family. About 500 species of Acacia are
distributed
over tropical and subtropical areas of Africa, India, Australia,
Central
America and southwest North America, but only a comparatively few are
commercially important. The important producing areas are the Republic
of the
Sudan, French West Africa, and several smaller neighboring African
countries.

As
mentioned
earlier, the trees produce gum arabic only when they are in an
unhealthy state
from poor nutrition, lack of moisture, or hot weather. The gum is
produced in
breaks or wounds in the tree bark, and exuded in the form of spherical
balls
resembling teardrops. These exudates are collected by hand by the local
natives
and transported to central collecting stations where they are sorted by
hand,
and exported gum suppliers in all Parts of the world. There the gum
arabic is
sorted again, ground, processed, and graded to meet various
specifications.

Standards

Minimum
standards for good
quality gum arabic have been defined in the Indian Pharmacopeia as
follows: 4%
total ash (maximum), 0.5% acid insoluble ash (maximum), and 1% water
insoluble
residue (maximum). In line with recent efforts to define standards for
food
grade additives, more rigid specifications have been established for
arabic,
karaya, and tragacanth, and published in the Food Chemicals Codex.
Ghatti has
not yet been included, probably because of its comparatively minor use
in
foods.

Structure

Gum arabic
exists in nature as a neutral or slightly acidic (D glucuronic) salt of
a
complex polysaccharide containing calcium, magnesium, and potassium
ions. It is
a heterogeneous material and may be composed of several slightly
different
molecular species. The most recent opinion is that the main structural
feature
of the molecule is a main chain of b galactopyranose units linked
through positions
1®3, with side chains of 1,6 linked galactopyranose units terminating
in
glucuronic acid or 4 0 methylglucuronic acid residues. Additional
groups are
also attached to the C 3 positions on the galactose side chains.
Complete
hydrolysis of the molecule yields the four basic sugar constituents D
galactose,
L arabinose, L rhamnose, and D glucuronic acid. These sugars are found
in gum
arabic from all species of Acacia, but the proportions vary among the
different
species. A recent study by Anderson has reported the presence of
methoxyl
groups in certain Acacia gums and suggested that the methoxyl content
has some
structural significance that has yet to be defined.

The
molecular
weight is believed to vary from about 250,000 to 1,000,000, and also
varies according
to the method of measurement. The shape of the molecule is believed to
be that
of a short stiff spiral, or coil, with the length of the main molecule
chain
varying between 1050 Å and 2400 Å according to the amount of charge on
the
molecule.

Properties

Solubility

Gum arabic
is
unique among the natural hydrocolloids because of its extremely high
solubility
in water. Most common gums cannot be dissolved in water at
concentrations
higher than about 5% because of their very high viscosities. Gum
arabic,
however, can yield solutions of up to 50% concentration. At these high
levels,
it can actually form a highly viscous, gel like mass similar in
character to a
strong starch gel. In addition to forming high solids gels of this
type, gum
arabic can be used at much lower concentrations in combination with
other gums
as thickeners and binders. Comparative viscosities of the common
natural plant
exudates are shown in Fig. 1 and Table 1.

Good grades
of
the gum give solutions that are essentially colorless and also impart
no taste
to the solution. Poor quality dark grades of arabic have an unpleasant
astringent flavor and odor, probably due to the presence of tannins.
These
should never be used in food products.

Gum arabic
is
insoluble in oils and in most organic solvents. It is soluble in
aqueous
ethanol up to a limit of about 60% ethanol. Limited solubility can also
be
obtained with glycerol and ethylene glycol.

Viscosity

Whereas
most
gums form highly viscous solutions at low concentrations of about 1 5%,
gum arabic
is unique in that it is extremely soluble and is not very viscous at
low
concentrations. High viscosities are not obtained with gum arabic until
concentrations of about 40 50% are obtained. This ability to form
highly
concentrated solutions is responsible for the excellent stabilizing and
emulsifying properties of gum arabic when incorporated with large
amounts of
insoluble materials.

The
viscosity of
gum arabic solutions will depend upon the type and variety of arabic
used.
Measurements of the relationship of concentration to viscosity made by
Taft
showed slight, but not unreasonable inconsistencies, considering the
differences in raw materials and methods of measurement. Their results
are
given in Table 2.

Rheological Behaviour

At
concentrations up to 40%, gum arabic solutions exhibit typical
Newtonian
behavior. Above 40%, solutions take up pseudoplastic characteristics as
denoted
by a decrease in viscosity with increasing shearing stress.

Effect of pH

The effect
of pH
on gum arabic solutions has been reported by several investigators who
tend to
agree that arabic acid is a strong monobasic acid. The viscosity of gum
arabic
rises sharply with increasing pH to a maximum at about pH 5 7, then
falls
slowly to about pH 10 14. The data reported by Thomas are shown in
Figure 2.
Normally, solutions of gum arabic are slightly acidic, having a pH of
about 4.5
5.5 and hence are in the area of maximum viscosity.

Effect of Electrolytes

The
addition of
electrolytes to a gum arabic solution results in a lowering of the
viscosity,
even in a very dilute solution. This lowering is much more pronounced
in more
concentrated solutions. The decrease in viscosity is proportional to
the
increase in the valence of the cation or the increase in the
concentration of
electrolyte. The addition of more than one electrolyte gives an
additive
effect.

This
lowering of
viscosity, which is accompanied by a lowering of the interfacial
tension,
produces favorable emulsifying conditions. Thus, while a good kerosene
water
emulsion can be obtained with a 10% gum arabic solution, equally good
emulsions
can be obtained with 0.5 % gum arabic solutions in the presence of
sodium
sulfate or sodium bicarbonate.

Effect of Aging

Studies on
solutions of gum arabic showed that all solutions underwent a decrease
in
viscosity with age. Unpreserved solutions showed the greatest drop in
viscosity, while solutions preserved with benzoic acid (0.2 %)
exhibited the
smallest loss of viscosity.

Compatibility

Gum arabic
solutions will produce precipitates with many salts, particularly
trivalent
metallic salts. It is incompatible with some gums, such as gelatin and
sodium
alginate, but quite compatible with methylcellulose,
carboxymethylcellulose,
and larch gum. In many cases, compatibility is subject to the influence
of pH
and concentration, and compatibility of gum arabic with other
components can be
obtained by proper adjustment of these parameters.

Emulsifying Properties

Gum arabic
is a
very effective emulsifying agent because of its protective colloid
functionality and has found widespread use in the preparation of varied
oil in water
food emulsions. It produces stable emulsions with most oils over a wide
pH
range and in the presence of electrolytes without the need for a
secondary
stabilizing agent. The gum arabic forms a visible film at the oil
interface,
but the mechanism of emulsification still is not understood. It is
believed
that arabic, as a film forming agent, prevents coalescence of the oil
globules,
thus permitting a high degree of dispersion by diminution of the
diameters of
the globules.

It has been
found that the chemical nature of the oil used can cause marked changes
in the
properties of acacia stabilized emulsions. The relative viscosity of
emulsions
made with gum arabic changed in accordance with the oil used as the
disperse
phase. It has been suggested that the differences might be due to the
presence
of a stabilizing layer, the thickness of which varied with the oil
used. This
layer is presumably large enough to contribute noticeably to the volume
fraction
and thus the emulsion viscosity.

A few other
minor gum exudates from fruit trees also have been said to have
excellent
emulsifying properties. Solutions (10%) of apricot, prune, and sweet
cherry gums
have been reported to have protective properties similar to a
comparable
solution of gum arabic, but since these gums are only available in
small
quantities in certain geographic areas, they have not been used in any
important food applications.

Plant Seed Gums

Almost all
important food plants produce seeds containing starch as the
carbohydrate
reserve. This starch serves as the principal food stored for use by the
embryonic plant in its initial growth stages. Many plant seeds,
however,
contain polysaccharide food reserves that are not starch (glucose
polymers),
but are polymers of other sugar molecules such as galactose and
mannose. These
polymers also have constructive hydrocolloid properties, and when
isolated, can
be used like gums from other sources.

While many
of
these seed gums are known and have been investigated, only a very few
of them
are important in the food industry, and at present only locust bean gum
and
guar gum enjoy a substantial degree of acceptance. Although psyllium
seed gum
and quince seed gum have also been utilized to some extent in the food
industry, they still find their most extensive uses in the related
pharmaceutical and cosmetic industries. The gums of flaxseed, tamarind
seed,
tara seed, flamboyant seed, and other seeds also have interesting
hydrocolloid
properties and may eventually prove to be economically and practically
suitable
in food applications.

As
mentioned
above, at present only locust bean gum and guar gum are of importance
as food
hydrocolloids with possible applications seen for psyllium seed and
quince seed
gums. This chapter will therefore be restricted to a discussion of
these gums.

Locust Bean Gum

Historical Background

The locust
bean,
or carob bean, plant is an ancient leguminous plant (Ceratonia siliqua
L.)
which is indigenous to the near East and Mediterranean areas. That it
has been
known for thousands of years is shown by the fact that the ancient
Egyptians
used carob paste for binding their mummies. Arabs used the carob seeds
or
kernels as weight stones to weigh precious metals and gems such as gold
and diamonds.
As a matter of fact, the word carat is cognate with the botanical name
ceratonia. Dioscorides, a Greek physician in the first century A.D.,
referred
to the curative laxative and diuretic properties of the carob tree
fruit.

In Biblical
times, the pods of the tree were widely used for feeding cattle,
horses, and
pigs (hence the name swines bread). The pods were used for human
consumption in
times of scarcity, and perhaps regularly by the poorer people. The
carob as
food was immortalized in the Bible in the passage where the sojourn of
St. John
the Baptist in the wilderness is described. His meat was locusts and
wild honey
is believed to refer to wild carobs (Matthew 3:4) and one of the names
for
carob bean that has lasted through the centuries is St. Johns bread, or
Johannisbrot. The Prodigal Son in the Bible also longed in vain to
feast on the
carob: and he would fain have filled his belly with the husks that the
swine
did eat and no man
gave unto him (Luke
15:16).

Even today,
the
Biblical meaning of carob trees is commemorated in a traditional Jewish
holiday. Jewish Arbor Day, TuBishvot, marks the tree planting season of
ancient
Israel and usually falls in February. It is the custom at this time to
eat and
display the fruits distinctive to Israel and one of the fruits honored
on this
occasion is the carob, or boksor as it is called in Hebrew.

The
importance
of carob as animal feed and human food slowly grew over the centuries
as the
tree was gradually introduced from the near East to other parts of the
world.
The Greeks were responsible for carrying it from Syria and neighboring
areas to
Greece and Italy while the Arabs, by virtue of their extensive
Mediterranean
trade routes, made the carob plant known in northern Africa and Spain.
In more modern
times, the carob was introduced to the Americas, Australia, and other
parts of
the world where climatic conditions were favorable to the cultivation
of the
plant.

The roasted
beans have been used extensively as coffee substitutes, especially in
Germany.
In North Africa the poorer inhabitants of the carob growing areas still
use the
pulp as a preferred sweet for children because of its high (30 to 50%)
sugar
content. During the Spanish Civil War in 1936 to 1939, the inhabitants
of the
carob growing area ate the locust bean as food. In southern Greece
during World
War II, after the German army had stripped the country of livestock and
most
other foods, the rural inhabitants lived largely on carob pods.

For several
years in the early 1920s there was considerable interest in California
in
various food products made from carob pods. Carob flour mixed with
wheat flour
was used to make an acceptable quality bread that was sold in the Los
Angeles
area for a short period. Another use was a sweet carob syrup with a
unique
flavor made by grinding the pods to a coarse powder, dissolving the
sugars with
water, and boiling the solution down to the thickness of honey.
Breakfast foods
made by beating the seedless pods into a powder were sold both as
straight
carob or mixed with wheat products according to the amount of fiber
desired.
Some very extravagant claims were made for the health and medicinal
properties
of some of these products until public interest waned. Today some carob
products are still being sold but mostly as a chocolate substitute in
health
foods. Recipes have been developed by suppliers for the use of carob in
cakes,
cookies, candies, ice cream, malted milk, and other foods in which
chocolate is
normally used.

Botany

The locust,
or
carob, tree (Ceratonia siliqua L.) is a member of the legume family and
is the
only species in the genus. It is a large, handsome evergreen tree, 40
50 feet
high, which has been used extensively for shade and avenue planting
throughout
southern California where the climate is similar to that of the
Mediterranean
countries where the carob tree thrives.

It is very
drought resistant and grows readily in areas where water is not
abundant.
However, it is a slow maturing tree and begins to bear fruit 5 years
after
budding and increases slowly to a maximum by the twenty fifth year when
the
tree is full grown. This feature of the carob tree is illustrated
interestingly
in an old Hebrew legend.

A famous
sage,
Honi ha Ma aggel, saw on his travels an old man planting a carob tree.
When
asked by the sage when he thought the tree would bear fruit, the old
man
replied, After seventy years. And dost thou expect to live seventy
years and
eat the fruit of thy labor? he was asked. The gentle reply was, I did
not find
the world desolate when I entered it, and as my fathers planted for me
before I
was born, so do I plant for those who will come after me.

Source

The locust,
or
carob, fruit itself has the shape of a long pod similar to a string
bean and
measures 4 12 inches in length, depending upon the variety. Within this
brown
pod are flinty, brown seeds approximately the size and shape of
watermelon
seeds. The weight of these seeds is 5 14% of the total weight of the
pod. These
seeds, or kernels, are the commercial source of locust bean gum, though
only
part of the seed is useful for that purpose. The seed is composed of a
central,
hard, yellow embryo germ portion (25 30%) that is surrounded by a large
layer
of white semi transparent endosperm (35 45%). This whole mass is in
turn
covered by a tenacious, dark brown husk, or outer coating (30 35%). The
endosperm contains the gum and is therefore the desired part of the
kernel.
Successful production of a high quality locust bean gum involves the
separation
of the endosperm from the germ and from the seedcoat.

In
commercial
practice, the husk is first removed by mechanical abrasion or by
chemical
processes. The dehusked kernels are then split lengthwise and the
endosperm is
separated from the germ or embryo. The isolated endosperm is then
finely
ground, graded according to accepted standards of color, impurities,
and
viscosity, and sold as commercial locust bean (or carob) gum. It is
obvious
that the purity and quality of the gum depends on the efficiency of the
separation of the endosperm from the other portions of the kernel.

Structure

Locust bean
gum
is a galactomannan polysaccharide with a molecular weight of about
310,000. The
structure is essentially a straight D mannose polymer linked C1 C4
with
relatively regular branching on every fourth or fifth mannose group on
C6 by
single D galactose units (Fig. 1). The ratio of D galactose to D
mannose seems
to vary according to reports from various workers, but this is believed
to be
due to varying origins of the gums and possibly to the stage of growth
or
development of the plant at time of gum production. The structure of
locust
bean gum is similar to that of guar and differs only in having a
smaller number
of D galactose side chains.

Properties

Locust bean
gum
is only partly soluble in cold water and must be heated in order to
achieve
optimum viscosity. Leo claimed that locust bean gum could be made
readily
soluble in cold water by intimately mixing 4 parts locust bean gum with
6 parts
corn sugar, then wetting, heating, steaming, drying, and finally
grinding to an
appropriate mesh size but
maximum
viscosity still required heating.

Normally,
in
order to obtain the greatest efficiency as a thickener, it is best to
disperse
the gum in hot water and then cool the solution. The solution is
extremely
viscous and sticky, and 1% concentration of a good quality gum may have
a viscosity
of about 3500 cps (Fig 2). One of the earliest recorded uses of this
property
was the use of locust bean paste by the Egyptians in preparing the
strips of
cloth with which they bound their mummies.

Since
locust
bean gum contains small amounts of insoluble protein and cellulose
impurities,
solutions of the gum show a cloudy, whitish opacity, which is a serious
drawback in food applications where clarity is desired.

Although
locust
bean dispersions or solutions in themselves do not gel, they have the
unusual
synergistic effect of imparting desirable elastic properties to
carrageenan and
agar gels. This effect is discussed in detail in the section on
carrageenan.

Since
locust
bean gum is a neutral polymer, its viscosity or stability is very
little
affected by pH within the range of pH 3 11. The chemical reactions of
this gum
are also similar to those of the other neutral polysaccharides. Its
esters and
ethers have been made commercially, some of which, such as the
carboxymethyl
ethers, have found interesting industrial applications but are not
permitted in
foods.

Applications

Ice Cream Stabilization

Locust bean
gum
has found an important application as a primary stabilizer in ice cream
mixes
because of its unusual swelling and water imbibing qualities, as well
as the
smooth meltdown and excellent heat shock resistance it imparts to the
final ice
cream product.

Cheese Products

In the
manufacture of soft cheese, locust bean gum speeds up coagulation,
increases
the yield of curd solids by as much as 10%, and makes separation and
removal of
the curd easier. The resulting curd has an excellent soft and compact
texture,
and the separated whey is limpid. The finished cheese has an excellent,
smooth,
resilient body and texture. It is also more homogeneous, and exudation
of water
from fresh cheese is reduced. These improved properties are believed to
be due
to the buffer function of the acidified locust bean gum solution, which
acts as
a protective colloid and maintains a constant pH in the finished cheese.

Cheese
spreads
and melted cheese products can be prepared from very soft cheese having
high
water content. The incorporation of locust bean gum ties up the water
and
results in a firm, spreadable texture and a highly homogeneous product
of fine
quality. It is even possible to add water to the cheese products if
desired.
The gum, usually used in a concentration of about 0.6%, is mixed with
other
ingredients, homogenized, pasteurized, and packaged in a stable form.

Meat Products

Locust bean
gum
has been used in the manufacture of processed meats such as salami,
bologna,
and sausages, where it acts as a binding and stabilizing agent and
yields a
more homogeneous product of improved texture and quality. It also has a
lubricating effect on the meat mix, facilitating extrusion and
stuffing. Due to
its water retention properties, locust bean gum reduces loss of weight
of these
meat products in storage. Locust bean gum has also been used as a
thickener for
canned meat and fish products.

In the
preparation of synthetic meat products, locust bean gum has been used
as an
important additive to contribute specific properties of meatlike
texture.
Protein food products simulating the nutritional and textural
characteristics
of meat were prepared from plant proteins extracted and isolated by
several
patented methods. The eating qualities of these chewy protein gels were
beneficially modified by the incorporation of locust bean gum as an
inner
additive to impart the essential meatlike chewiness.

Bakery Products

Locust bean
gum,
used to supplement flour in the manufacture of bread and other leavened
bakery
products, produces doughs with constant functional properties and good
water holding
characteristics. Higher yields are obtained and the baked products have
better
textures, are much softer, and have a longer shelf life.

Addition of
the
gum to cake and biscuit doughs also gives higher yields and a
considerable
saving of eggs. Further, the cakes and biscuits are softer and have a
longer
shelf life. The cakes have a firmer texture, are easily removed from
the cake
pans, and are cut or sliced without difficulty.

Neukom
investigated the effect of periodic acidoxidized locust bean gum on the
dough
and baking characteristics of wheat flour. It was assumed that the
introduction
of reactive groups (aldehydes) into the polysaccharide molecule would
result in
further reaction with flour proteins, leading to an increase in the
toughness
and rigidity of the dough. Locust bean gum, with, degrees of oxidation
varying
from 10 to 100% of theoretical, were incorporated into wheat flour at
levels of
0.1 0.5% of flour weight. Dough properties were measured on the
Brabender
Extensograph, and bread baking tests were also made. At a certain
concentration
level, the oxidized locust bean gum distinctly improved the dough
properties. The
extensibility and resistance of the doughs could be manipulated to give
values
which from experience, are considered to be brought about by flour
improvers.
Neukom and Deuel concluded that these modified polysaccharides react
with the
flour constituents, and that the improving effect is enhanced as the
degree of
oxidation is increased (i.e., as the number of aldehyde groups
introduced into
the polysaccharide is increased).

In pies,
locust
bean gum has been found to be a very satisfactory stabilizer for canned
berry
and berry apple pie fillings. In frozen pie fillings, it has also
performed
satisfactorily in conjunction with certain starches. Carlin also
suggested its
use in stabilizing meringue toppings for pies in order to increase
shelf life.

Miscellaneous

In special
purpose
dietetic foods, locust bean gum has often been used for various
purposes.
Arobon, a locust bean gum preparation, has been added to infant diets
for the
treatment of diarrhea. Martins suggested using locust bean gum
(Nestargel) as
an additive at 0.25 0.50% levels in fresh or dried milk in order to
increase
the product viscosity, thus giving the consumer a higher degree of
satiety
without increasing caloric content.

El Sokkary
found
locust bean flour to be an effective antioxidant for butterfat when
added to
ghee (processed butter) at levels of about 0.5%. It was believed that
the gum
exerted a synergistic effect upon the natural antioxidants in the
butter.

Stevens
used
locust bean gum to stabilize citrus juice products, i.e., to maintain
the
natural cloudiness of the citrus fruit beverages, or at least to make
it last
longer. Recommended use levels for this application in citrus beverage
concentrates were about 1 30 ppm locust bean gum, preferably in
combination
with 20 400 ppm sodium hexametaphosphate.

Katz used
locust
bean gum in preparing a base material for frozen desserts and
confections. The
base material, which was capable of floating on water, was a mixture of
a bland
tasting edible oil, sugar, locust bean gum, and propyl 3,4,5
trihydroxybenzoate,
in the form of a solid, aerated slab. Another aerated dessert,
developed by
Mancuso, was based on gelatin, with locust bean gum or guar as an
additive. A
mixture of gelatin, locust bean gum, partially degraded soy protein,
sugar, and
an organic acid forms an aerated, flavored, chiffon type of gel dessert
when dissolved
and whipped in hot water, and then allowed to set.

Locust
bean gum continues to be
used as an effective thickening agent in salad dressings and various
types of
sauces.

Gaur Cum

Historical Background

Guar gum is
derived from the seed of the guar plant. Cyamopsis tetragonolobus, of
the
Leguminosae family. This plant has been grown for thousands of years in
India
and Pakistan where it is a most important crop that has been long used
as food
for humans and animals. Some guar seeds have even been found in a
recently
excavated tomb of an ancient Egyptian pharaoh.

Although
guar
was well known in Asia, it was not introduced into the United States
until 1903
when it was evaluated as a possible cover crop in the Texas, Arizona,
and
California areas by the United States Department of Agriculture.
However,
little interest was shown at the time, and until the advent of the
Second World
War, very little headway was made in the cultivation of the plant in
this
country. At that time supplies of locust bean gum, which was widely
used in the
paper and textile industries and usually imported from Europe and North
Africa,
became more and more limited and difficult to get. Therefore,
interested
groups, made a concerted effort to find a domestic plant that could
provide a substitute
for locust bean gum. This search led to the reexamination of guar gum,
and guar
was found to be the best answer to the problem.

In 1945,
because
of its extensive milling experience, General Mills undertook a study of
guar,
with respect to: (1) agricultural production of the plant in the
southwest, (2)
milling, and (3) adaptation of the product to industrial requirements.
It was
not until 1953, however, that the gum was produced in commercial
quantities.
Stein, Hall & Co., as well as General Mills, built plants in
the United
States for domestic production of guar gum, and some time later, the
European
producers of locust bean gum also began to process guar gum.

Source

The guar
plant
is a pod bearing, nitrogen fixing legume. The seeds of the plant are
composed
of the hull (14 17%), germ (43 47%), and endosperm (35 42 %). In the
manufacture of guar gum, the endosperm must be separated as cleanly as
possible
from the hull and germ. In practice, there are several methods for
accomplishing this. The
hull can be
removed by treatment with sulfuric acid to loosen it, by heating and
charring
the hull by flame treatment, or by mechanical grinding and sifting.
After the
hull is removed, differential grinding is used to separate the germ.
The
endosperm and germ can be separated in this manner because of the
difference in
hardness of each constituent. After the endosperm is separated from the
hull
and germ, it is ground to a fine particle size and sold as guar gum.
Various
trade names are often used for guar, such as Jaguar, Supercol, and
Guartec.

Structure

Guar gum,
like
locust bean gum, is a galactomannan. But there are significant
differences in
their chemical structures and properties. Guar is structurally composed
of a
straight backbone chain of D mannopyranose units with a side branching
unit of
D galactopyranose on every other unit. Locust bean gum differs in this
branching structure by having an average of one D galactopyranose unit
branch
on every fourth D mannopyranose unit (Fig. 1). The greater branching of
guar is
believed to be responsible for its easier hydration properties as well
as its
greater hydrogen bonding activity. Guar gum has an average molecular
weight in
the range of 200,000 300,000.

Pectins

The word
pectin
is derived from the Greek phctoV meaning to congeal or solidify. The
actual
chemical compound was discovered by Vauquelin in 1790, but it was not
truly
characterized until Braconnot first described it as the principal
gelling agent
of fruit and gave it the name pectin. Braconnot understood that pectin
was the
substance that gave fruits the ability to form jellies when boiled with
sugar.
He also recognized that sugar and the proper pH were necessary for the
reaction, and he mentioned that he had to add a small amount of acid
(hydrochloric
or sulfuric acid) to break up the pectates when making his jellies.

After
Braconnots
work on pectin, a great deal of scientific research was done during the
next
century from both the chemical and biological points of view.

Nomenclature

As a result
of
the vast amount of confusion that had been created over the years by
various
investigators in the field, the American Chemical Society finally
adopted a
standard nomenclature for these materials in 1927. The standard was
later
revised and broadened in 1944. Pectin was then defined functionally as
those
pectinic acids capable of forming the standard type of fruit jellies
when sugar
and acid were present in the correct proportions.

The uniform
definitions adopted at that time and still in use today are as follows:

Pectic
substances are those complex colloidal carbohydrate derivatives that
occur in,
or are prepared from, plants and contain a large proportion of
anhydrogalacturonic acid units, which are thought to exist in a
chainlike
combination. The carboxyl groups of polygalacturonic acids may be
partly
esterified by methyl groups and partly or completely neutralized by one
or more
bases.

Protopectin
is
the water insoluble parent pectic substance that occurs in plants and
which on
restricted hydrolysis, yields pectin or pectinic acids.

Pectinic
acids
are the colloidal polygalacturonic acids containing more than a
negligible
proportion of methyl ester gropps. Pectinic acids, under suitable
conditions,
are capable of forming gels in water with sugar and acid, or, if
suitably low
in methoxyl content, with certain ions. The salts of pectinic acids are
either
normal or acid pectinates.

Pectin (or
pectins) are those water soluble pectinic acids of varying methyl ester
content
and degree of neutralization and are capable of forming gels with sugar
and
acid under suitable conditions.

Pectic acid
is a
term applied to pectic substances composed mostly of colloidal
polygalacturonic
acids and essentially free from methyl ester groups. The salts of
pectic acids
are either normal or acid pectates.

Protopectinase
is the enzyme that converts protopectin into a soluble product. It has
also
been called pectosinase and propectinase.

Pectinesterase
(PE), or pectinmethylesterase, is the enzyme that catalyzes the
hydrolysis of
the ester bonds of pectic substances to yield methanol and pectic acid.
The
name pectase does not indicate the nature of the enzyme action and has
given
way to these more specific names.

Polygalacturonase
(PC), or pectin polygalacturonase, is the enzyme that catalyzes the
hydrolysis
of glycosidic bonds between de esterified galacturonide residues in
pectic
substances. Pectinase is frequently used to designate the glycosidase
as well
as pectic enzyme mixtures.

The pectic
substances, which are all modifications of galacturonic acid polymers,
can be
differentiated by the degree of methoxyl substitution
this is
the current accepted industry practice. Thus, Bender groups commercial
pectins
into five distinct categories according to their degree of methylation
(DM):
(1) 30 DM pectin for low sugar gels (2)
45 DM pectin for rapid setting, calcium precipitatable pectin suitable
for high
sugar gels and emulsions (3)
60 DM or
slow set pectin for high sugar gels and confectionery jellies (4) 74 DM for typical rapid
set pectin for
jams and jellies (5)
higher DMs for
special purpose applications.

McCready,
however, prefer a simpler, though arbitrary, classification of gelling
pectins
into three groups: (1) rapidset, (2) slow set and (3) low methoxyl. The
boundary
lines are not sharp, and the distinction between the three groups seems
to be
related to their solubility and degree of esterification (DE): (1)
rapid set
pectin 70% DE or higher (2)
slow set
pectin 50 70% DE (3)
low methoxyl pectin
–50 % DE or lower.

An
even simpler classification,
which is preferred and used herewith by the author, is to consider just
two
types of pectin: (1) regular pectins which require sugar and acid for
gelling,
and (2) low methoxyl pectins which have methoxyl contents below 7% and
require
calcium for gelation.

Function in Plants

The pectic
substances, in combination with cellulose and starches, are structural
components of all green land plants. Although they are found mainly in
fruits
and vegetables, traces have also been discovered in cereals where their
contribution to structure is of minor importance.

Pectic
substances are integral components of the cell structures and function
as
cementing substances in the middle lamellae. They are present in the
various
stages of molecular development and transformations, which are
dependent on the
specific morphology, and taxonomy of the plant as well as the stage of
growth
and maturity. The chemistry and interrelationship of these materials
(pectins,
pectinic acids, pectic acids) are still not completely elucidated and
therefore
continues to be the subject of continuing research by many scientific
groups in
all parts of the world.

The
function of
pectins in fruits and vegetables is primarily concerned with the
retention of
form and firmness of the plant. Pectins also seem to play a role in the
control
of the movement of water and plant fluids through the rapidly growing
plant.
The action of pectins as intercellular substance in plants is similar
to the
action of intercellular substance of animals, e.g., collagen, the
precursor of
gelatin. Protopectin, the water insoluble precursor of pectin, is
abundant in
immature fruit tissues. The normal process of ripening and maturing
involves
hydrolytic changes of protopectin to form pectin, followed after
maturity by
enzymatic demethylation and depolymerization of pectin to form pectates
and
eventually soluble sugars and acids.

In a
similar
manner, nature has provided not only enzymatic means for pectin
breakdown in
plants but has also provided the human digestive system with a somewhat
similar
enzymatic mechanism to digest the pectins normally ingested as a part
of
natural fruitstuffs. This ease of digestibility of pectic substances is
quite
different from that observed for the hydrocolloids derived from natural
land
and sea plants. Most of the gum exudates from trees or bushes have an
aldobionic acid nucleus for the gum structure that is very difficult to
break
down. The seaweed extracts also consist of gel forming polyuronides
with
complex nuclei that are very resistant to hydrolytic breakdown. The
pectic
substances, on the other hand, can be broken down quite easily by
digestion.

In general,
the
pectins of fruits at very early stages of growth are almost completely
methylated and have a very high molecular weight. As growth proceeds
and the
fruit matures, pectic enzymes are believed to attack the pectin and
hydrolyze
it into smaller polymers with lower methoxyl contents, higher carboxyl
contents, and lower molecular weights. As the fruit continues to mature
this
catabolic process continues. Commercial pectin is usually extracted
when the
pectin still has a relatively high methoxyl content and molecular
weight.

Structure

Pectin, a
fairly
complex heterogenous structure, is composed chiefly of
polygalacturonide chains
having a wide variety of molecular weights. Some of the carboxyl groups
are
esterified with methyl alcohol, some are neutralized with cations, and
some are
free acids. In addition to variations in its molecular weight and
methoxyl
content, pectin may also vary with respect to the distribution of ester
groups
along the chains. Small amounts of acetate and other groups are also
sometimes
attached to the molecule.

The pectic
acid
molecule consists of D galacturonic acid units in pyranose
configuration linked
together by a 1, 4 glycosidic linkages. In nature, the carboxyl groups
are
partially methylated to form the ester known as pectin. In addition,
the
secondary hydroxyl groups may be partially esterified by acetic acid.
Thus the
degree of esterification in natural products may vary within a wide
range.

The pectin
macromolecules may be changed by saponification or esterification. The
configuration and relationship of the basic pectic acid molecule to
cellulose
and alginic acid is shown in Fig. 1.

Properties

The
properties
of the pectic substances depend greatly on their molecular weight and
their
degree of substitution. Properties such as water solubility, viscosity,
coagulability, gelling tendency, and stability toward enzymes change
directly
with increasing degree of esterification. These changes can be
explained by the
alteration of the electric charge and the form of the pectin
macromolecules.
Solubility of pectin decreases with an increase in chain length and
with a
decrease in methoxyl groups.

Viscosity

The
viscosity of
pectin solutions depends on several factors, namely, the DM of the
pectin,
concentration, temperature, pH, and presence of salts and their
concentration.
Decreasing the concentration or the grade of pectin increases the
viscosity, as
would be expected. Temperature changes decrease the viscosity in a
similar
manner. However, if alkaline earth salts are present in pectins of 60
DM or
lower, the decrease might be larger than expected.

Effect of pH

Even when
sufficient pectin and sugar are present in the system, no gel will form
until
the pH is reduced below the critical value of about 3.6 known as the
limiting
pH value. Most slow setting pectins give optimum performance at pHs
between 2.8
and 3.2, while rapid setting pectins perform best in a range of 3.0
3.4. The
effect of pH is not entirely predictable, since it depends upon the DM
and any
salts that may be present. The tendency of a 30 45 DM type of pectin to
gel
would be decreased by a change in pH and prevented by lowered pHs.
Solutions or
dispersions of pectinic acids free of alkaline earth salts will
increase in
viscosity and finally gel at very low pHs.

The effect
of
added alkali metal salts such as sodium chloride is also not very
predictable.
The salt effect depends on the amount of salt, the type of pectin, and
the pH
of the solution. Small amounts of sodium chloride (as low as 0.6%) will
produce
a great increase in viscosity or gelation of a 0.8%, 40DM pectin
solution when
the pH is 2.9. But the viscosity will be decreased at a pH of 4.4. At
still
higher pHs (about 6) salt effects are minimized if phosphates are also
added.
It is believed that viscosity is solely dependent on the length and
shape of
the chains.

Effect of Calcium Salts

The effects
of
calcium salts on pectin viscosity are very important. These effects
show up as
an increased viscosity even for pectins of 75 DM or higher, and show a
maximum
viscosity at pHs of 8.55. The viscosity increasing effect of added
calcium ions
increases sharply as the degree of methylation decreases, thus freeing
more
carboxyls for cross linking of the chains by calcium ions. The
increased
viscosity is very evident at 60 DM and becomes greater as the DM
increases
until it reaches a maximum of 80.

In general,
it
can be stated that pectins of the same type can be compared with
respect to
viscosity when they are in solutions of the same grade, pH,
temperature, and
salt content. Viscosities of different pectin types can also be
compared, but
even small variations in pH or salt content of the media can noticeably
change
the final viscosities.

Low Methoxyl Pectins

Low
methoxyl
pectins, as opposed to regular pectins, do not require sugar for gel
formation
and are also not as sensitive to pH. On the other hand, they are
sensitive, to
divalent metallic cations such as calcium.

Effect of Cations

Divalent
metal
ions can react with carboxyl groups from adjacent pectinate chains to
form a
gel network. This ionic cross linking by normal valence forces of
divalent ions
can be slowed down temporarily by such monovalent ions as sodium which
can also
react with the free carboxyl groups. Usually, the effect of such ions
is to
curtail the cross linking reaction of calcium and to improve the
solubility of
low methoxyl pectin in the presence of calcium. Sometimes a better gel
results
when salts such as sodium citrate are present in low concentrations.

Sugar

Low
methoxyl
pectins can form gels without the need for sugar, but the presence of
small
amounts (10 20%) of sugar tend to impart desirable textural properties
to these
gels. High concentrations of sugar (60% or higher) interfere with gel
formation
because the dehydrating effect of the sugar favors hydrogen bonding and
decreases cross linking by ordinary valence forces. It is therefore
important
to determine the optimum sugar level for any specific gel application.

pH

Low
methoxyl
pectin gels can be prepared within a comparatively wide pH range. Good
milk
gels can be made at pHs up to 6.5, while fruit or vegetable gels can be
made at
pHs as low as 2.5. The practical and most desirable range for most
salad and
dessert gels is 3.2 4.0. Regular pectin gels have a limiting pH near
3.5 above this,
gels cannot be formed.

Temperature

Temperature
is
an important factor in the formation of low methoxyl pectin gels. Low
methoxyl
pectin will form gels that are much more stable at much higher
temperatures
than can be made with other gelling systems such as gelatin. The
temperature of
gel formation and the stability of the gel will depend upon the initial
gel
composition. Gels made with high concentrations of pectin, such as
tomato
aspics, will form and be stable at temperatures of 120 150°F, while
gels using
low levels of pectin are not stable at temperatures above 100°F.

Gel Formation

Theoretical Discussion

Commercial
grade
pectin has the unique property of dispersing in water to form a viscous
colloidal sol, which will gel in the presence of appropriate
concentrations of
sugar and acid. The structure of these pectin sugar acid gels is
entirely
different from that of gelatin, and indeed, the mechanism involved in
pectin
gel formation is also quite different.

Seaweed Extracts

Botany

Algae,
which
belong to a major division of the plant kingdom, are composed of those
nonseed
bearing plants that contain photosynthetic pigments. The plants, which
may vary
in size from single cells to giant conglomerates, all share a common
anatomical
feature in the absence of a vascular or food conveying system. Since
the plants
must be submerged in the medium from which they acquire their food,
they are
found in ponds, lakes, and streams and in the salt seas and oceans
where they
attain maximum size. The larger forms of these plants are known as
seaweeds,
although they are not really weeds, but flowers of the sea as the poets
have
described them.

During the
millenia of evolution, several parallel evolutionary branches of these
marine
algae developed, each branch using different pigment systems for
photosynthesis. The largest and most numerous forms are the two major
groups
comprising the red and brown algae, while the smaller groups consist of
the
green and blue green algae, which are confined, in general, to fresh
water
regions.

All plants
contain structural substances that hold the various cells together and
that
form a large proportion of the plant weight. These substances are
usually
hydrocolloid polymers composed of sugar units. In land plants, neutral
polymers
such as cellulose and hemicellulose are the major components, while in
sea
plants, the structural polymers are the more flexible, negatively
charged
polyelectrolytes.

The red
algae,
or Rhodophyceae, contain predominantly red pigments and are the source
of
several important hydrocolloids, namely agar, carrageenan, and
furcellaran, all
of which are polymers of galactose. The second important group is the
Phyophyceae, or brown algae, which contain predominantly brown
pigments. The
largest and most numerous of the brown algae are commonly referred to
by the
inclusive term kelp, a term generally reserved for those forms growing
in large
masses such as the floating giants of the Pacific coast.

The major
hydrocolloids of the brown seaweeds are the salts of polyuronic acids
(mannuronic and guluronic acids). The soluble salts of this polymer,
such as
sodium salts, are generally referred to as algins. Any salt of the
polymer is
an alginate, while the organic salts or esters are called algin
derivatives.

The
important
seaweed species that are used for the production of commercial seaweed
extracts
are shown in Table 1. These are not all inclusive, and undoubtedly
other
botanical species are often used, but in general, these specific types
of red
and brown algae form the basis of the industry today.

Historical Background

The
utilization
of seaweeds for food and medicine can be traced as far back as 3000
B.C. when
Shen Nung, a famous oriental physician used the plants for their
medicinal
value. Later, in the time of Confucius the food uses of seaweed were
lauded in
the Chinese Book of Poetry, which extolled a housewife who cooked
seaweed.

There is
little
doubt that agar was the first seaweed hydrocolloid isolated as an
extract from
the parent plant. It had been known in oriental countries for ages and
was used
in the form of a sweetened, and sometimes flavored, gel. The use of
agar for
foods and the extraction of similar gel forming seaweed extracts, were
probably
spread through the Orient and the western Pacific areas by the various
migrations of the Chinese and Japanese. In areas such as Indonesia and
the
Philippines, the native weeds were exploited in a similar manner by the
inhabitants, and a great deal of intercultural applications of the
extracts
were developed as evidenced by the host of colloquial names still in
use for
similar seaweed extracts.

In the
western
world, the seaweeds utilized were those found off the coasts of Europe,
Africa,
and North America and were mainly the carrageenan bearing red seaweeds
and the
algin bearing brown seaplants.

Carrageenan,
in
many respects, was to the Occidentals what agar was to the Orientals.
It was known
for many years in the seacoast areas of Ireland, Great Britain, France,
Norway,
and other European countries. And its vernacular name, Irish moss is
quite
indicative of its origins in the coastal Irish town of Carragheen
whence its
current name carrageenan is derived.

The
importance
of the carrageenan seaweeds to these various geographic communities is
difficult to assess. Although they have been used locally for
centuries, it was
not until the nineteenth century that they became an article of
commerce. And
it has only been in modern times that they have been extracted as a
pure
hydrocolloid. Prior to this carrageenan was eaten as a whole plant or
extracted
indirectly by the housewife who wanted to make a pudding of the blanc
mange
type. During the Irish potato famine in the middle of the nineteenth
century,
these Chondrus crispus seaweeds were used to make a not very nourishing
St.
Patricks soup.

Algin or
sodium
alginate first became a commercial product due to the perspicacity of
an
English chemist, who observed that the viscous fluid found in the
blisters or
sacks on the surface of kelp plants was a unique substance of
remarkable
properties. Although his initial commercial venture was not successful,
Stanford had sown the seed of a new industry. Today alginate products
are
manufactured in various parts of the world and are standard commodities
of
trade.

Furcellaran,
the
most recent seaweed hydrocolloid to achieve commercial importance in
the food
industry, was a result of the search for agar substitutes during World
War II.
As the story goes, a barber in Denmark was investigating various kinds
of
seaweeds in an effort to make a permanent wave liquid product. He found
that
the seaweed Furcellaria fastigiata, which is found off the coast of
Denmark,
gave a shiny, gummy material with good thickening properties. This
discovery
was commercialized. The extracts sold as Danish agar are now used in
sizeable
quantities in the food industry.

Today, with
the
ever growing realization that the sea is the last remaining great food
resource
on earth, a great deal of research is being done to find new seaweed
extracts
of commercial use. Many plants and extracts are being studied, and
undoubtedly
many new hydrocolloids will become available in the future for food
applications.

Structure

Red Algae

The red
algae
are quite different from higher plant forms because large amounts of
sulfated
polysaccharides are accumulated in the cell walls or intercellular
regions. The
nature of the polysaccharide sulfate from each alga is distinctive and
characteristic of each plant type and is useful for the classification
and
differentiation of the algae. For example, the polysaccharides of the
Rhodophyceae usually contain galactose as the D
or
as the D and L
enantiomorphs, often together with such
derivatives of each enantiomorph as the 3,6 anhydride, the 6 0 methyl
ether
and/or various sulfate esters.

A major
variation that has been consistently observed among red seaweed
extracts is in
ester sulfate content this may range from as low as 0% in the agarose
fraction
of agar to as high as 36% in carrageenan. The common red seaweed
extracts have
the following amounts of ester sulfate:

Anderson in
their studies of the red algae structure have come to the conclusion
that a
close relationship exists between many of these polysaccharides, and
that the
same basic structure is common throughout many of these polymers. This
structure is, namely, a chain of galactose units linked alternately a
l,3 and b
1,4. This basic structure is modified by different algae to produce
many
variations on the same structural theme. They differ from each other in
having
either the D or L configuration, the 3,6 anhydro group, the ester
sulfate
group, or by being methylated. These variations alone can yield
thousands of
possible compounds.

As the
basic
structures of these various seaweed gums become more accurately
defined, it
begins to appear that all of the seaweed gums may be composed of a
common group
of basic building blocks that form different types of polymers
according to the
type of plant and its stage of growth or development. This least common
denominator theory is being investigated by studies of enzymes which
might have
exact specificities for the various building blocks in the molecules.

In summary,
it
would appear that the sulfated galactans of the red seaweeds are a
family of
related polymers, each with properties appropriate for a particular
species
growing in a particular environment.

Brown Algae

Alginic
acid is
the only important extract of brown algae at this time. It was
considered to be
primarily a polymer of anhydro l,4 ,b D mannuronic acid until Fischer
established the presence of L guluronic acid in the hydrolysis products
of
alginic acid. Based on this and other confirmatory work, alginic acid
is
currently regarded as a polyuronide comprising D mannuronic and L
guluronic
acids, the relative proportions of which vary in different species of
brown
algae.

The
building
blocks or molecular entities that have been isolated and identified in
the four
commercially important seaweed extracts are shown in Table 2.

Agar

Historical Background

In spite of
its
Malayan name, agar agar is of Japanese origin and was first fully
exploited in
Japan. According to Tseng, Chinese settlers in the East Indies
introduced the
use of Japanese agar as a food to the natives. To avoid a Chinese or
Japanese
name, they called it agaragar, a name used by the Malayans to indicate
certain
seaweeds and the jellies made from them.

In Japan
itself,
agar is called kanten, meaning cold sky. This name refers to the fact
that the
material used to be prepared on cold winter days or high up in the
mountains
where it was always cold. In other areas it is also known as Japanese
isinglass, Chinese isinglass, vegetable isinglass, seaweed isinglass,
Japanese
gelatin, bar kanten, square kanten, slender kanten, tungfen (frozen
powder),
and many other colloquial names common to specific geographic areas.

The Dutch
and
other Europeans living in Indonesia later learned to use this Japanese
product
for making fruit and vegetable jellies and seem to have introduced this
art of
jelly making to their friends and relatives in Europe.

But it was
not
until 1882 that the world wide fame of agar was truly established when
Robert
Koch introduced the product into bacteriology as a culture medium. Koch
himself
did not realize the importance of this discovery as a major technical
improvement, for in his famous experiments on the isolation of the
tuberculosis
bacillus, he disposes of this new culture medium in a single,
insignificant
sentence, So wachsen sie beispielsweise auf einer mit agar agar
bereiteten, bei
Blutwaren hart bleibenden Gallarte, welche einen Zusatz van
Fleischinfus und
Pepton erhalten hat.

The
credit for first using agar
as a culture medium rightly belongs to a housewife, Frau Fanny Hesse,
who had
been using agar for years in her kitchen for the preparation of
jellies. She
had received the recipe from Dutch friends living in Indonesia. When
her
husband, Dr. Walther Hesse, complained about the difficulty of using
gelatin in
cultivating microbes, she suggested agar instead. His successful
application
was communicated to the famous Dr. Koch, who in turn, introduced it to
the
world. The rest is history. Today, almost a century later, agar is
still the
best culture medium available. The gelling and colloidal properties
that make
agar the excellent bacteriological medium are the ones that have been
utilized
in various food applications, as will be discussed later.

Collection of Agar Weed

In Japan,
the
agar bearing seaweeds are gathered from rocks between mid and low tide marks, or else
divers collect
them from the sublittoral regions. In certain areas of Japan, the
collection of
seaweed by diving has developed into a unique industry largely carried
out by
female divers. These diving, girls, known as amas, inhabit the Chiba
prefecture
(province) along the seacoast. They are trained from early childhood to
dive
for various seaweeds. The word ama originally meant the sea and was
used for
calling the divers when the boats were full. These women operate from
rafts,
boats, or even large wooden tubs, which are paddled to the collecting
areas.
There, they dive for the weeds and store them in the tubs or rafts.
When
sufficient material has been collected, the tubs are towed to shore by
the
women who swim with them. These bare breasted women develop an
abnormally large
chest expansion and lung capacity and would probably do well in
Hollywood if a
seaweed shortage should occur. They use no equipment except goggles and
operate
in water depths down to 30 feet. In deeper waters, below 60 feet, male
divers
equipped with diving apparatus gather the harvest. After the weed has
been
collected, it is dried on the shore and partly bleached. It is then
sold to
manufacturers for final processing. The deep water weed is considered
to yield
the best gelling extracts, and the optimum harvesting time is from
April to
September.

Processing

Background

For
centuries,
agar was produced by simply boiling seaweeds to obtain a jelly mass.
The modern
method of purification and preparation was discovered by accident.

According
to legend, it was in
the year 1658 or thereabouts that the Emperor of Japan and his royal
party were
caught in a sudden snowstorm and took refuge in a nearby inn. The
innkeeper Tarozaemon
Minoya by name prepared a dish of
seaweed jelly for his royal guests. The left over jelly was thrown
outdoors,
and it froze solid during the night. The next day, when the sun came
out, the
frozen jelly thawed and the watery part drained off, leaving a dry,
papery,
translucent substance. The acute innkeeper found that this residue
could be
remade into a jelly by boiling it up with more water. The new jelly was
clearer
and of better quality than the original product.

This
discovery
was subsequently adopted by producers of agar. The process of purifying
agar
seaweed extracts by consecutive freezing and thawing operations became
a
standard procedure that is still used in commercial practice today in
Japan.

Current Process

All
commercial
agar is manufactured essentially by hot water extraction followed by
freeze thawing
for purification. Agar weeds appropriate to give a final product of
desired
properties are blended in carefully predetermined proportions. The
batch of
weeds is soaked and washed with fresh water and then extracted by
boiling in
water in open iron kettles or by pressure autoclaving in modern plants.

At some
point,
calcium hypochlorite or sodium bisulfate is introduced in order to
bleach, or
decolorize, the agar so as to obtain the lightest possible product. The
extract
is filtered hot and the residue is re extracted one or two times. The
extract
is allowed to cool, and when gelled, the solid mass is allowed to
freeze
naturally or is frozen by refrigeration. The frozen gel is allowed to
thaw, and
the impurities are drained off with the excess water. The gel is then
dried,
ground, and packed for shipment.

Structure

The
structure of
agar has been studied for many decades, primarily by Japanese
scientists, some
of whom have spent their entire professional lives in this area of
research.

Araki was
the
first to isolate agarose, and subsequent work by other workers led to
the
currently fairly well established opinion that agar is a mixture of at
least
two polysaccharides–agarose, a neutral polymer, and agaropectin, a
sulfated
polymer. The ratios of these two polymers vary widely and the
percentage of
agarose in agar bearing weeds can range from 50% to 90%. The two
polymer
components can be fractionated either by acetylation in chloroform to
give a
soluble agarose acetate and an insoluble agaropectin acetate or by
selective
precipitation of the agaropectin with quaternary ammonium salts.

Microbial Gums

Anthropologists
know of no society in which fermentation has not been employed to make
life
more pleasant. The cave man discovered that meat allowed to age a few
days
after the kill was more pleasing to the taste than meat eaten
immediately. He
also learned that intoxicating drinks could be made from rotting grains
and
fruits. These two unconscious uses of the fermentation process, the
aging of
meat and the manufacture of alcohol were the first applications of what
today
is a vast science. To primitive man, fermentation was a type of magic.
He was
not aware that he was using the natural activity of tiny living
organisms, such
as molds and yeast, to improve the taste and texture of his foods. But
without
knowing that these creatures existed, ancient man learned how to put
them to
work. For thousands of years, the soy sauces of China, Japan and other
oriental
countries were made from fermented beans. For centuries, the Balkan
peoples of
Europe enjoyed fermented milk or yogurt, while in Central Asia, the
nomadic
tribesmen enjoyed an alcoholic beverage called kumiss, made from
fermented mares
or camels milk. The preparation of one of mans oldest foods, bread,
which has
been used in some form virtually everywhere on earth, involves
controlled yeast
fermentation.

The
discovery of
fruit fermentation by which wine is made, was made so long ago that the
ancient
Greeks believed that wine had been invented by the god Dionysus. Beer
was also
an ancient discovery, and a Mesopotamian clay tablet written about 500
years
B.C. tells that brewing had been a well established profession for
several
thousand years. Beer was also a commodity that the Babylonian Noah,
Utanpishtim, took on board his ark to make his trip more pleasant.
Egyptian
documents dating back to the Fourth Dynasty (about 2600 B.C.) describe
the
malting of barley and the fermentation of beer, and it is well known
that the
Pharaohs enjoyed a cloudy, unreliable beer made in this fashion. A
Chinese rice
beer, kiu, has been traced back to 2300 B.C. More recently, when
Columbus
landed in Central America, he found that the Indians drank a beer made
from
corn.

During the
middle Ages, experimenters learned how to improve the taste of wine,
bread,
beer, and cheese, but they had no idea that they were dealing with a
form of
life too small to be seen by the naked eye. The true cause of
fermentation was
not understood until the latter part of the nineteenth century when
Louis
Pasteur arrived on the scene.

The change
from
art to science, which was initiated by Pasteurs discovery that
fermentation is
brought about by living yeast cells, signaled the beginning of a new
era, which
in the last 100 years has wrought such miracles as the discovery of
penicillin,
streptomycin, and other antibiotics, as well as the food additives that
help
make our foods more nutritious and appetizing.

In the area
of
hydrocolloids, fermentation technology has also played an important
part in the
development of polysaccharide gums having unique functional properties
that are
capable of making important contributions to the food industry.

Dextran

Background

Microbial
polysaccharides can be roughly divided into two groups
homopolysaccharides and
heteropolysaccharides. The homopolysaccharides include those polymers
produced
from sucrose by a variety of bacteria, of which the best known members
are the
dextrans.

The term
dextran
was first used to describe the slimy material formed in the juices of
sugar
beets, wine, and other sugar based food products. It was a well known
nuisance
in the sugar industry because it sometimes clogged up the pipes through
which
sucrose containing juices and solutions were transferred. Pasteur
showed that
these slimes were caused by microbial action. Shortly thereafter,
Scheibler
found that dextran is a carbohydrate with the empirical formula
(C6H10O5) x.
Since the material was closely related to starch and dextrin, he coined
the
name dextran for it. Later investigations showed that dextran can be
formed by
many microorganisms and is not a well defined substance with specific
properties. It is more accurate to refer to dextrans when no clear
definition
of the bacterial origin and chemical properties of the substance are
given.
Much work on these microorganisms was erratic due to the study of
impure
preparations, but comparatively recently Hucker
classified the microorganisms
responsible for producing dextran from sucrose. The main dextran
synthesizing
bacteria belong to the Leuconostoc genus, species mesenteroides and
dextranicum, tribe Streptococceae, and family Lactobacteriaceae.
Subsequent
work isolated other strains of bacteria that are capable of producing
various
dextran materials. All of the species, however, have one common
characteristic,
in that sucrose is the only suitable carbohydrate source for the
manufacture of
the polysaccharide. The organisms can grow on any medium containing
sucrose,
together with a few inorganic salts and a suitable source of nitrogen.

From the
large
number of microorganisms capable of synthesizing dextran, it was seen
that one
of the factors determining the properties of the polysaccharide
obtained was
the strain of the particular bacteria used. Likewise, the final
structure of
dextran obtained was closely related to the particular strain that
produced it
and it appeared that individual strains of bacteria have the ability to
mutate
over the years to the extent that the branches on the resultant
polysaccharides
eventually become attached at points on the main chain different than
those
found originally. Most of the work with dextran has been conducted on
material
produced by various strains of Leuconostoc mesenteroides, which was
also given
the designation B 512. Among the different types of bacteria that can
produce
dextrans, the Leuconostoc mesenteroides strain has been most thoroughly
studied, and most scientific investigations are based on dextrans of
this
origin.

Production

The
formation of
dextran depends upon dextran sucrase, an enzyme of the dextran
producing
microorganism. This enzyme is active outside the bacteria cells and
passes into
the culture medium either through secretion or autolysis of the cells.
Dextran
can therefore be produced either by the cultivation of these organisms
or by
synthesis using the cell free enzyme extract. Only the first method has
been
used in large scale industrial production.

The
production
of dextran by cultivation of Leuconostoc mesenteroides is carried out
at
suitable temperatures and pH in a fluid medium containing sucrose,
nutritional
substances necessary for the growth of the bacteria, and the buffer
material,
which limits the pH displacement during fermentation.

The process
takes place in two phases. First, the bacterial cells divide, releasing
the
dextransucrase into the medium. Second, the enzymatic polymerization of
glucose
units to dextran takes place. Gradually, as the dextran is formed, the
medium
thickens into a tough, viscous mass. When the viscosity is greatest,
the
maximum yield is obtained, and the dextran is precipitated by the
addition of
methanol, ethanol, or acetone. The white, rubberlike precipitate is
then dried
and pulverized to give a white to slightly yellowish dextran
hydrocolloid.

Parameters
that
influence the type of dextran obtained are the following: (1) strain of
the
organism, (2) optimum pH of the synthesis, (3) incubation time, (4)
manner of
innoculation, (5) composition of the culture medium.

Structure

Structural
studies by Sloan have shown the dextran produced by B 512 to contain
95% of
(1®6) linked units of a D anhydroglucopyranose, and 5% of (1®3) linked
units.
Van Cleve subsequently demonstrated that the B 512 dextran contained a
repeating segment of approximately 23 anhydro D glucopyranosyl units.
Of these,
21 units are (1®6) linked, 1 unit is a branch (1®3) linked, and 1 unit
is an
end group. About 80% of the external branches are only one D glucose
unit long.
A typical structural segment is shown in Fig. 1.

The
molecular
weight of the polymer is dependent upon the fermentation medium. If no
primer
or acceptor is present, the dextran formed has a molecular weight of
more than
100,000,000. If a primer such as maltose is used, the dextran molecules
will be
predominantly below 50,000 molecular weight. If a dextran primer of
15,000 40,000
is employed, the majority of the resultant dextran will have a
molecular weight
of 75,000±25,000, the preferred type for use as a blood extender.

Properties

Dextran is
a neutral
polysaccharide, readily soluble in hot or cold water to give clear,
viscous
solutions. It is tasteless, chemically inert, and compatible with most
ingredients normally used in foods.

It has
typical
hydrocolloidal characteristics such as emulsifying and stabilizing
properties
in oil water systems. It is also known for its humectant and water
holding
qualities, and it imparts effective bodying attributes to liquid foods.

The
chemical
structure, due to its low degree of branching, affords a high degree of
stability to hydrolytic depolymerization, which makes it useful as a
synthetic
blood plasma extender.

Physiologically,
dextran, when ingested, is hydrolyzed slowly to form absorbable
carbohydrates,
which are utilized. This was shown by feeding tests on animals and
humans.
Dextran, given by mouth, produced a modest but sustained increase in
blood reducing
substances and liver glycogen. The evidence suggested that the
intestinal
breakdown of dextran is not ascribable only to bacterial action, but
more
likely to an enzyme or enzymes present in the intestinal mucosa.

More
recently,
Baker reported that biological tests demonstrated that when dextran
containing
a high proportion of a (1®6) linkages is included in a normal diet on a
regular
regimen, gain in body weight is inhibited. Even though dextran is
edible and
assimilated without unfavorable effect on the human system, it appears
that the
a (1®6) linkages are resistant to attack by bacteria and enzymes
present in the
gastrointestinal tract. This may suggest its use in low calorie foods
or
reducing diets.

Applications

Medical

Dextrans
have
been proposed for use in a large number of industrial and medical
applications,
but the greatest use has been in medicine where partially hydrolyzed
dextrans
have successfully been used as blood plasma extenders in the treatment
of
shock. For this application, a dextran possessing a molecular weight in
the
range of 50,000 100,000 is required, and a great deal of experimental
work has
been done to produce dextrans in this range.

Baked Goods

Bohn found
that
the incorporation of small quantities of dextran in yeast raised bread
doughs
containing both yeast and gluten produced breads that were softer and
had a
greater volume and longer shelf life than ordinary breads made from
doughs
without dextran. The dextrans preferred were derived from Leuconostoc
mesenteroides and had molecular weights of about 20,000,000 40,000,000.
The
amount of dextran used ranged from about 0.01 10% by weight of the
flour
contained in the dough. The addition of dextran to the doughs increased
the
water absorptive properties of the resultant dough and also made the
dough more
extensible by softening the gluten.

Toulmin
prepared
edible containers, such as ice cream cones, from dextran. The dextran
was mixed
with sugar, milk, and water or oily plasticizer to give a mash that
could be
molded and baked in the usual manner after forming.

Beverages

Hamburg
used
dextran to replace 10 20% of the malt in the production of pilsener
beer. The
dextran beers were reported to have good flavor and foam stability and
had the
same color as pure malt beer. The carboxymethyldextran derivative is an
effective foam stabilizer when added to beer or other fermented malt
beverages
at about 0.5% concentrations.

Dextran has
been
used as a stabilizer for chocolate milk beverages. Mahoney also found
it
effective in the stabilization of the soft drinks and flavor extracts.
Likewise, Wadsworth found it to be useful in the production of
noncrystallizing
sugar syrups where stability and viscosity were important qualities.
Dextran
has also been suggested for use as a bodying agent in low calorie,
sugar free
beverages.

Confectionery

Mahoney
described dextran as a desirable constituent for use in all foodstuffs
in which
there is a sugar component. Its value was in its capacity to prevent
crystallization, improve moisture retention, improve body, and maintain
flavor
and appearance. It was effectively used in candies, fondants, jellies,
and
canned fruits.

Wadsworth
subsequently combined the entire sterile culture liquor of dextran with
sucrose
syrup to prepare a noncrystallizing sugar syrup of exceptionally high
viscosity.

Corman used
purified dextran sucrase to convert a sucrose solution enzymatically to
a
higher viscosity, fruit additive, dextran syrup, containing all the D
fructose
originally present in the sucrose molecule. The product had enhanced
sweetness
and superior odor and flavor over that from the whole culture process.
Viscosity could be controlled by reaction conditions and by the
addition of the
dextransucrase.

Preservative Coatings

Dextran has
been
employed for preserving a large variety of foods by preventing the food
from
drying out during storage and by protecting it against the deleterious
effects
of exposure to air.

Toulmin
used an
aqueous solution for dispersion of native or hydrolyzed dextran to
preserve
shrimp and other products. Similarly, other foods, such as meats, dried
fruits,
and cheese, could be coated with a film of dextran, which protected the
food
against drying in storage, and yet permitted the product to vent the
gases.

Novak used
aqueous dextran dispersions containing antibiotics as a preservative
coating
for quick frozen foods, such as fish or spinach. The dextran film
lengthened
the storage life and retarded decay during thawing by absorbing and
moisture.
In a similar manner, Woodmansee and Abbott coated sub scalded chicken
broiler
parts with dextran to protect them against dehydration and skin
darkening in
fresh storage.

In work
with the
carboxymethyldextran derivative, Novak found it to be effective as a
flavor
fixative. Citrus oils emulsified in gelatin to prevent deterioration
are
protected against insolubilization of the gelatin by incorporation of
less than
1% of carboxymethyldextran. In a related fashion, coating monosodium
glutamate
crystals with carboxymethyl dextran offers protection against potency
loss and
agglomeration of the granular material.

Miscellaneous

Owen
suggested
the use of dextran as a conditioner in chewing gums as well as a
stabilizer in
ice cream products. It could also be used in the manufacture of
frostings and
synthetic creams. In general, dextran could replace, in whole or in
part, such
gums as gum arabic, karaya, locust bean gum, tragacanth, or alginates.

Polysaccharide
B 1459 (Xanthan Gum)

Background

The
successful
work on the fermentation of sucrose to produce dextran (B 512) led to
concerted
efforts by the Northern Utilization Research and Development Division
to find
other microbial polysaccharides that might be industrially useful. They
were
particularly interested in using glucose (corn sugar) as a fermentation
medium,
since one of the functions of the Northern Regional Laboratory at
Peoria,
Illinois, was to find new uses for the agricultural crops in that area,
of
which corn was a major one.

The
laboratories
were quite successful in achieving their objective. One new gum,
Polysaccharide
B 1459, had such interesting properties that several industrial
companies
investigated the possibility of commercializing it. The Kelco Co.
started producing
it commercially under the trade names Kelzan (industrial grade) and
Keltrol
(food grade), while Archer Daniels Midland Co. carried it through
advanced
development stages as Product 7097 and patented an improved biochemical
process
for synthesizing it. Two other large companies, Eli Lilly & Co.
and
Commercial Solvents Corp., also explored the commercial potential of
this
material for food, drug, and cosmetic applications, but apparently the
product
did not go into production. The Jersey Production Research Company
found the
gum to be a very effective water and brine thickening agent for oil
well
drilling operations and developed a new and novel process for making it.

Gelatin

The above
epigraph aptly describes one of the most popular and widely eaten
American
foods gelatin desserts. The shimmering, tender texture and brilliant
clarity of
a quality gelatin dessert have widespread esthetic as well as
organoleptic
appeal to a broad majority of consumers. And the properties of gelatin
that
lend themselves to the preparation of such gelled food products are
unique and
cannot be exactly duplicated by any other hydrocolloid. This has given
gelatin
a tremendous advantage in the area of packaged dessert mixes, so that
today the
majority of gelatin produced in this country is used in dessert foods.

Gelatin is
defined in the Pharmacopeia as a product obtained by the partial
hydrolysis of
collagen derived from the skin, white connective tissue and bones of
animals.
The fact that gelatin is obtained with ease and in relative purity from
an
abundant starting material probably has much to do with the fact that
it has
become the classic protein of colloid chemistry, and has been the
subject of an
enormous amount of experimental work.

Of all the
common natural hydrocolloids, gelatin is the only protein of
importance,
largely because of its novel gelling and thickening properties.
Recently, with
advances in technology, other protein gums are becoming subjects of
interest
for the hydrocolloid chemist. The most important of these are the soy
proteins,
which, like gelatin, also have interesting and exploitable gelling,
thickening,
and other colloidal properties. Egg albumin, a relatively old protein,
is being
given new functional properties, which permit its use in a much wider
variety
of foods. In addition, the milk protein caseinates have been found to
have very
effective emulsifying and stabilizing proper properties, while cereal
proteins
make excellent whipping agents.

However,
since
gelatin is by far the most important protein hydrocolloid, this chapter
will be
limited to gelatin.

Background

Gelatin,
derived
from the Latin verb gelare meaning to congeal, has been known for
thousands of
years. The extraction of glue by cooking hides dates back at least to
the time
of the ancient Pharaohs of Egypt. Bogue cites a 3000 year old stone
carving,
found in the ancient city of Thebes and belonging to the period of
Thotines
III, which describes the gluing of a thin piece of rare red wood veneer
to a
yellow plank of sycamore.

Later, in
the
Roman era, Pliny, Lucretius, and others referred to the manufacture of
glue.
Pliny wrote, Glue is cooked from the hides of bulls. Elsewhere in his
writings
he referred to glue, which had been mixed with gums, milk, eggs, and
wax as a
vehicle for paints, used by the ancient Egyptians. Much later, in the
Elizabethan period, Shakespeare and Bacon made frequent references to
glue in
their writings. Indeed, a commercial glue industry appears to have been
established in England about 1700. A similar industry developed in the
United
States within the following century.

During the
early
years of the Napoleonic era, gelatin was manufactured on a large scale
in an
attempt to alleviate the food shortages resulting from the English
Naval
blockade of Europe. The first manufacture of edible gelatin is credited
to
Arney, who was granted a patent in 1846 for the preparation of a
powdered
gelatin for forming compositions from which may be prepared jellies and
blanc
manges also, when
mixed with falina, or
starch, or starchy vegetable flour, for thickening soups, gravies, etc.
At
present, gelatin is manufactured in the United States by at least
eleven
companies in the amount of about 60 70 million lb annually.

Collagen

Collagen,
which
means glue producing material, is the principal protein component of
the
connective tissues, which serve as the major stress bearing elements
for all
mammals and fishes. Although much of the collagen is located in major
tissues
such as skin, tendon, and bone, collagen fibers pervade almost every
organ and
tissue. Collagen is unique among proteins because of its unusual amino
acid
composition. It owes its distinctive structure to its high content of
the
cyclic amino acids, proline and hydroxyproline. In addition to these
compounds,
collagen also contains large quantities of glycine and alanine, the
more common
nonpolar amino acids with short side chains.

It is now
believed that proteins consist of long chains of amino acids connected
through
their a amino and a carboxyl groups to form peptide linkages

These
chains can
be either stretched out or folded. Additional bonds, between adjacent
chains or
between adjacent parts of the same chain after folding, become a
necessary part
of the structure and stabilize the functional protein configuration.

The basic
collagen polymer unit, sometimes called tropocollagen, is thought to
consist of
three helical polypeptide chains wound around each other to form a
coiled coil,
which behaves as a firm, rigid rod. Recent work indicates that
irrespective of
source, collagen has a molecular weight of about 350,000, a length of
3000Å,
and a diameter of about 14Å. As shown in Fig. 1, it has now been
established
that two types of bonds contribute to the secondary and tertiary
structure of
collagen: (1) intramolecular cross links existing between the
individual chains
of the collagen molecules, and (2) intermolecular cross links.

The gross
collagen fibers are capable of undergoing considerable mechanical and
physical
changes, which may vary from reversible swelling and partial, melting
to
irreversible disorganization of the entire structure. But all these
changes
occur without solubilization of the fiber.

Transformation of Collagen to Gelatin

Gelatin is
the
water soluble product of the dissolution or degradation of water
insoluble
collagen fibers. The transformation or transition of collagen to
gelatin is the
process whereby the highly organized, quasi crystalline, water
insoluble
collagen fiber is transformed from an infinite assymetric network of
linked
tropocollagen units to a system of water soluble, independent molecules
with a
much lower degree of internal organization. Since the original collagen
structures are not all the same, and since there are many paths by
which the
structure may be broken down, there are obviously a great many
varieties of
gelatin formed by the destruction of collagen.

The
hydrogen bonded
configuration of the collagen macromolecule can be broken down by
heating
collagen solutions in acid to about 40°C. The transition is sharp and
complete
within a few minutes over a small temperature interval, and the
disordered
molecule falls apart in one of three ways, as shown in Fig. 2.

1.
If there are no additional
restraining bonds between chains, three randomly coiled single strand
peptide
chains result (Path 1). The three chains, known as a chains, are not of
identical composition and probably not of equal molecular weight.

2.
In those cases (Path 2) where
two chains are joined by one or more covalent cross linkages,
denaturation
leads to the appearance of two particles, one an a chain and the other
a two stranded
molecule with approximately twice the molecular weight of the a chains.
The two
stranded b component may be composed of two similar or two dissimilar a
chains.
The weight distribution would be 67% b and 33%a.

3.
In the final case, it can be
assumed that at least two covalent cross linkages hold the three chains
together. The disordering process (Path 3) melts out and removes all
traces of
secondary structure, but the three chains cannot separate and remain as
a unit
in solution. This three chain structure is called the g component.

It is
obvious
that there is no reason why every molecule of tropocollagen should have
the
same number of identically disposed intramolecular cross linkages, and
thus, it
is most reasonable to assume that any given preparation is
heterogeneous with
respect to the degree of intramolecular polymerization. The ideal
conversion of
the collagen monomer to gelatin is therefore the one via Path 1. The
number average
molecular weight of the gelatin system should be one third the
molecular weight
of the collagen monomer, and the weight average molecular weight should
be
slightly higher due to the nonidentity of the chains. The best values
of the
collagen monomer molecular weight are substantially above 300,000, and
hence
the minimum molecular weight of the parent gelatin must be greater than
100,000. Reports of lower molecular weights for gelatin probably
indicate that
peptide bond hydrolysis was a factor in those studies. Reports of the a
gelatin
having molecular weights of about 80,000 are not consistent with recent
studies
on acid soluble collagen.

Therefore,
it
can be assumed that native collagen fiber is an ordered array of
parallel
tropocollagen rods, staggered by approximately one fourth of their
length. Each
tropocollagen rod is composed of three chains of a character but
probably of
different chemical composition, and may contain intra tropocollagen
cross linkages
to produce the b sub unit of two chains or the g units with bonds
joining each
of the three chains. All g units may not be of the same degree of
intramolecular polymerization and may in addition be bonded together
with
interunit cross linkages to form g polymers.

Manufacture of Gelatin

The bulk of
gelatin manufactured is derived from three basic sources and consists
of two
types of finished gelatin product. Type A gelatin is derived from acid
processed
materials, primarily pork skin. Type B gelatin is derived from
alkaline, or
lime processed, materials, primarily cattle hides and bone (ossein). In
Europe,
a substantial quantity of type A gelatin is made from ossein.

Sources

a.
Pig Skins. One of the major
sources of gelatin in the United States is pig skins. They are frozen
just
after removal at the meatpacking plants and delivered to the gelatin
plants in
refrigerated cars. Since some of the fat remains on the skins, it is
preferable
to process these by acid pre treatment in order to avoid forming a
soapy
emulsion that would make extraction of the gelatin extremely difficult.

b.
Cattle Hides (Tanners Stock).
These are calf or cattle hide trimmings not usable for the manufacture
of
leather. The whole hides are shipped to tanners and the trimmings from
the
hides in various stages of the process, before actual tanning, are used
by the
gelatin manufacturer.

c.
Ossein (Bone). Although this
is one of the best known gelatin raw materials, it is the one least
used in the
United States. Ossein is the residue of dried cattle bones remaining
after acid
pre treatment to remove the calcium phosphate. Even though ossein is a
very
expensive raw material, if properly processed, it makes an excellent
gelatin
for photographic use and one that can command higher prices.

Processing

The
manufacture
of gelatin is shown in the flow diagram in Fig. 3. In general, all
gelatin is
manufactured by one of the two following processes or modifications
thereof.

Acid
Processing (Type A)

Acid
processing
is usually based on the use of pig skins and ossein, and the most
important
commercial acid process in the United States is the preparation of
edible
gelatin from, frozen pig skins. The pig skins are thawed, washed in
cold water,
and soaked in approximately 5% solutions of inorganic acids. This
plumping
process hydrates and swells the skin without causing appreciable
solubilization.

Hydrochloric
acid, sulfuric acid, phosphoric acid, and sulfurous acid are the most
frequently used acids. The acid soak usually takes 10 30 hours, after
which the
supernatent acid is removed and cold water is used to wash away the
excess acid
and raise the pH of the soaked skins to about pH 4. Most of the
noncollagenous
proteins have isoelectric points in the pH 4 5 range and are thus most
readily
coagulated and removed. The acid conditioned skins are then subjected
to a series
of hot extractions where the two variables are time and temperature.
The
initial extraction (first run) is carried out for the longest time at
the
lowest (about 60°C) temperature. The temperature is raised about 5 10°C
in each
successive extraction and five to ten extractions may be made. In
general, the
gelatin made from the first extract excels subsequent extracts in gel
strength,
and each run is kept separate and blended later to match various
requirements.

The dilute
gelatin extract is pressure filtered and concentrated by vacuum
evaporation.
The warm concentrated solution is then cooled almost to its gelling
point,
poured onto a belt conveyor, and immediately conveyed into a
refrigeration
chamber where it is chilled rapidly until it gels. Upon emerging from a
refrigerator chamber as a continuous sheet, it is cut into suitable
lengths and
placed on wire frames, which are then placed into a drying room or
drying
tunnel, where the temperature is carefully controlled. Continuous
dryers are
now in use where both temperature and humidity are controlled. The rate
of
drying is closely regulated to avoid melting or surface dehydration.
When the
moisture has been reduced to approximately 10%, the gelatin is removed
and
ground or pulverized to form the final product. Each batch of dried
gelatin is
graded and stored separately. Gel strengths and viscosities are the
criteria
for grading and the different grades of gelatin are blended to give a
finished
product with the desired specifications.

Alkali
Processing (Type B)

Bones are
initially demineralized with dilute acid to remove the calcium salts,
particularly the phosphate, and then both the ossein and cowhides are
treated
in a similar manner. The raw collagen stock is washed and thoroughly
hydrated
in cold water in large tanks or pits. Excess water is drained and lime
is added
in sufficient amounts so that when fresh water is added a saturated
solution of
calcium hydroxide is formed. An excess of calcium hydroxide must be
maintained
to make up for the amount consumed in the conditioning reactions. The
hides are
left in the liming pits for periods of 3 12 weeks or longer, depending
upon the
nature of the stock, ambient temperature, type of operation, alkalinity
of the
lime liquors, etc.

The lime
treatment removes most of the extraneous albuminoids such as globulins,
mucopolysaccharides, albumins, as well as carotenes and various other
pigments.
After liming is complete, the lime is washed from the surface of the
stock with
running water for a day or so. The residual base is then neutralized by
washing
with dilute hydrochloric acid until the collagen is deplumped, or until
it
becomes limp and flaccid. At this point, the collagen has a pH of 5 8
and is
ready for conversion to gelatin.

The
collagen
stock is then loaded into extraction kettles and gelatin is extracted
in a
series of cooks at successively higher temperatures. The highest
quality
gelatins are obtained in the first few extractions and the liquors from
each
cook are filtered, concentrated, and dried separately as for the Type A
gelatins. Again, the overall balance of viscosity and gel strength for
any
particular quality of gelatin is usually achieved by blending gelatins
from
several different extractions.

Final Products

While all
gelatins have similar functional properties, there are differences
between the
Type A and Type B gelatins, which are important in the selection of the
appropriate gelatin for any specific application. These differences in
physical
properties are shown in Table 1 and will be discussed in more detail in
the
following sections.

Chemical Composition

Amino Acids

Gelatin
consists
of 19 amino acids joined by peptide linkages to form long polymer
chains. It
gives a typical protein reaction and may be hydrolyzed by any of the
proteolytic enzymes to yield its constituent amino acid or peptide
components.
Gelatin is not a nutritionally complete protein in that it is lacking
in the
essential amino acid, tryptophan. However, it contains a small amount
of the
rare amino acid hydroxylysine. Gelatins from different sources may
exhibit
small variations in amino acid composition, as shown in Table 2.

The
variations
in chemical structure between the Type A and Type B gelatins produce
differences in the physical properties, including the isoelectric and
isoionic
point.

Gelatin is
an
amphoteric substance, i.e., one that has both acidic (carboxyl) and
basic
(amino, guanidino) groups. The overall charge of the molecule depends
upon the
pH of the solution and other ions present. The pH at which the
ionization of
both the acidic and basic groups are equal is called the isoionic point
(pI).
At this point, the net charge is zero. If electrolytes are added to the
solution, this point may be shifted to a new pH. This new pH, known as
the
isoelectric point (IEP), is defined as the pH at which gelatin
molecules do not
migrate in an electrical field (because they are neutrally charged at
that
point). In some cases, the pI and the IEP are identical.

Ash

Ash yielded
by
gelatin varies with the type of raw material and the method of
manufacture.
Type A or pork skin gelatins contain small amounts of chloride, while
ossein
gelatin contains principally calcium phosphates. The J.P. limit on ash
is 2%,
but most commercial gelatins have lower ash contents.

Metal Content

The metal
content
of gelatin is rigidly controlled, and the presence of such materials in
gelatins is unlikely unless impure acids or chemicals are used in the
process
of manufacture. The D.S.P. limit for arsenic is 1 ppm and for heavy
metals 50
ppm. Most gelatins meet these requirements without difficulty.

Sulfur Dioxide Content

The
addition of
sulfur dioxide gives hard gelatin capsules an increased transparency,
greater
brilliancy, and improved stability all qualities that are desired in
capsule
manufacture. The J.P. permits not more than 0.004 % sulfur dioxide in
most
cases, but for gelatin used in capsules, as much as 0.15 % is
permitted.
However, these are special grade gelatins that are not used in normal
food
consumption.

Cellulose Gums

The history
of
hydrocolloids in foods has until very recently been the story of
natural
materials derived from seaweed extracts, tree and bush exudates, plant
seed
flours, and similar sources. Almost all these natural materials are
polysaccharides or mixtures of polysaccharides. Today a new and growing
category of gums, which is still in its infancy, is that of the
chemically
modified natural gums. Although these man modified polymers are
currently only
a small fraction of the total gum market (food and industrial) about
100 million
lb of the total 3 billion lb of water soluble gums sold domestically
they are
steadily pressing at the position of the natural gums and enlarging
their
foothold in the field as newer and better modified hydrocolloids become
available.

Proponents
of synthetic
gums, pointing to the giant advances of organic chemistry, feel that as
silk
was replaced by nylon, rubber by neoprene, waxes by plastics, so the
natural
gum polymers are targets for the organic research chemist. Although
exact
duplications may not be possible, or even desirable, a sufficient
number of the
functional properties of the natural materials can be reproduced by
chemical
synthesis or modifications to create marketing opportunities for these
new
materials.

Modification
of
inexpensive natural materials such as cellulose and starch yields
synthetic
gums that have many of the properties of natural gums. They also have
the
advantages of low cost, steady and inexhaustible supply, constant
uniform
properties, tailor made functionality designed to meet specific
applications,
domestic availability, and sometimes new unique properties not
available in
natural gums. Moreover, pure synthetic gums, derived from the
proverbial coal,
air, and flame of the ancient alchemists, are also being created, some
of which
are already being used as food additives. These materials, usually much
more
expensive to make, offer the promise of completely novel hydrocolloids
for new
technological breakthroughs.

As starting
materials, the organic chemist has available two of natures cheapest
and most
abundant raw materials starch, at about $0.06 0.09 per pound, and a
cellulose
pulp, at about $0.09 0.14 per pound. Both of these readily available
polysaccharides are excellent starting materials for the production of
gums.
They both can be chemically modified easily by heat, oxidation, or
chemical
treatment. Proper control of the modification makes possible a great
variety of
products. As Whistler pointed out, it is conceivable that as more is
learned
about the relationship of structure to the physical properties of
polymers,
specific gum properties will probably be custom tailored into starch
and
cellulose molecules so that the properties of the custom made products
will
more closely match the properties desired in special gum applications.
Caution
is urged, however. It must be remembered that although sophisticated
chemical
procedures may modify a polysaccharide to give the desired end product,
the
materials and processing costs may be so high that the new gums will
not be
competitive in price with the natural gums. This chemical modification
of
natural polysaccharides is both a stimulating challenge for industrial
chemists
and a substantial protective barrier for the lowercost natural gums. It
is
probable that in the foreseeable future, chemically modified starches
and
celluloses, as well as the purely synthetic gums, will continually
compete with
the natural gums for the expanding markets for these materials.

In 1961, as
previously mentioned, the traditional market for watersoluble gums was
estimated to have been 3 billion lb. Of this total, the largest
percentage by
far was held by the natural gums, including the starches, whereas only
about
100 million lb were composed of the synthetic gums. However, this
compilation
is not complete, since it does not include data on such hydrocolloids
as
Gantrez An, Polyox, Carbopol, and other newer and less well known gums.
In
addition, estimates of the potential market for water soluble films
alone range
up to 20 million lbs per year.

In the food
industry, the chemically modified and synthetic gums at present occupy
a minor
role. Of the total market of 100 million lb in 1961, only an estimated
12
million lb was consumed by the food industry. The modified or synthetic
gums
used in foods were chiefly well established gums such as carboxymethyl
cellulose
and methylcellulose. The newer chemically synthesized polymers will
have a
difficult, up hill, and expensive battle to develop markets in the food
industry because the stringent Food and Drug Administration regulations
require
extensive animal feeding tests and experimental assurance of
nontoxicity before
allowing their use as food additives. As a result, most companies
developing
water soluble gums tend to look for industrial applications and strive
to
develop profitable markets in these nonfood industries before
attempting to
penetrate the food industry. The ease of penetration or acceptance is,
of
course, dictated by the novel and unique functional properties offered
by the
new gum that cannot be matched by the current available ones, or by the
simple
advantage of a cost reduction or product quality improvement.

Cellulose Derivatives

Cellulose
is the
major constituent of most land plants and is the most abundant natural
material
in the world. Together with the hemicelluloses and lignins, it forms
the cell
walls and intercellular layers, which are the primary structural
support for
the plant.

The purest
natural cellulose is cotton fibers or linters, which on a dry basis
consist of
about 98% a cellulose. Wood contains about 40 50%, and together with
cotton
linters, it is the most important commercial source for raw material
cellulose.
Agricultural residues, such as corn stalks, corncobs, and wheat straw,
contain
about 30% cellulose and are available as a vast reservoir of
potentially
available raw material.

The
cellulose
molecule is composed of a chain of repeating cellobiose units, each of
which consists
of two anhydroglucose units it
can be
more briefly described as a linear polymer of b D glucopyranose (Fig. 1
with R
= H).

Physicochemical
studies have shown the degree of polymerization of cellulose to be
greater than
3000 so that, with the spatial arrangement of the glucose residues, the
molecules are long and threadlike. X ray measurements, however, show
that in
native cellulose, the molecules are aligned to form fibers, some
regions of
which are highly ordered and have a crystalline structure due to
lateral
association by hydrogen bonding. The crystalline regions vary in size
and
represent areas of great mechanical strength and high resistance to
attack by
chemical reagents and hydrolytic enzymes. The physical and chemical
properties
of cellulose are largely dependent on the relative amount and
arrangement of
the crystalline regions. The cellulose molecules tend to remain
extended but
may normally undergo a degree of turning and twisting. Because of its
size and
strong associative forces, it can only be brought into solution under
certain
conditions, usually by chemically modifying the polymer and forming
cellulose
derivatives. In this way, many diverse and useful functional properties
can be
imparted to the cellulose molecule.

As with
many
other notable discoveries, the first chemically modified cellulose
polymer was
made by accident. Christian Schonbein, a professor of chemistry at the
University of Basel in 1846, was conducting some experiments in his
kitchen.
The flask in which he had been distilling nitric and sulfuric acids,
accidentally broke and the corrosive liquid spilled all over the floor.
As the
story goes, Schonbein, unable to find a mop, wiped up the mess with his
wifes
cotton apron, which he then washed and hung up over the hot stove to
dry.
Instead of drying, however, the apron flared up suddenly and
disappeared.
Schonbein had invented guncotton (cellulose nitrate). This accidental
discovery
was a major factor in the advances of polymer chemistry and stimulated
the
development of many other synthetic cellulose derivatives.

The
cellulose
derivatives commonly encountered in the food industry are ethers in
which alkyl
or hydroxyalkyl groups have been substituted upon one or more of the
three
available hydroxy groups in each anhydroglucose unit of the cellulose
chain.
The effect of the substituent groups is to disorder and spread apart
the
cellulose chains so that water or other solvents may enter to solvate
the
chain. By controlling the type and amount (degree) of substitution, it
is possible
to produce products that have a wide range of functional properties.

In addition
to
derivatives of cellulose made by chemical substitution, a modified
cellulose
made by acid hydrolysis has recently been developed that has functional
gum
properties. This hydrolyzed cellulose, called microcrystalline
cellulose or
Avicel, has found novel uses in the food industry, primarily in low
calorie
foods. Although not soluble in water, Avicel has a great water
absorptive
capacity. Thus it functions as an effective thickening and bodying
agent
similar to many hydrocolloids.

Properties

Avicel

Cellulose
and
starch are both condensation polymers of glucose. The differences in
linkages
between the glucose units however are sufficiently great to cause great
differences in properties. Pure cellulose is substantially insoluble in
water,
while starch can be readily dissolved in hot water.

However,
recent
developments in cellulose technology have led to the preparation of
pure a cellulose
products, which have hydrophilic properties and which can function as
hydrocolloids in various food applications. One of the most important
of these
products is a microcrystalline a cellulose sold under the trade name of
Avicel.
The normal a cellulose found in natural plants is a fibrous material,
which
does not absorb water and is comparatively inert under most conditions,
while
Avicel, a specially hydrolyzed a cellulose, is nonfibrous and has water
absorptive properties.

Avicel is
prepared by the acid treatment of a cellulose under special processing
conditions, as disclosed by the patent of Battista. By controlled
hydrolysis
with hydrochloric acid, a cellulose is converted to two components an
acid soluble
fraction and an acid insoluble fraction. The acid insoluble crystalline
residue
is washed and separated. It is called cellulose crystallite material or
microcrystalline cellulose. Essentially, the amorphous regions of the
polymer
are hydrolyzed completely, leaving the crystallite regions as isolated
microcrystallites, which are defined as the level off degree of
polymerization
cellulose, or DP cellulose. In other words, if the hydrolysis reaction
were
continued, the degree of polymerization would not change, indicating
that the
level off period or limit of reactivity, has been reached. The reported
level off
DP consists of 15 375 anhydroglucose units, the constituent chains of
each
aggregate being separate from those of neighboring aggregates. These
aggregates
are characterized by sharp X ray defraction patterns indicative of a
substantially crystalline structure.

The
commercially
available microcrystalline cellulose comes as a white, fine flour which
is low
in ash, metals, and soluble organic materials. It is insoluble in
water, dilute
acid, common organic solvents, and oils. It is partially soluble, with
some
swelling, in dilute alkali. Table 2 summarizes the chemical and
physical
properties of this material.

Avicel RC

A major
drawback
of this Avicel product has been the fact that it requires a great deal
of
energy to completely disperse and hydrate the dry material. In
addition, in
many food applications, the incorporation of large amounts of Avicel
gives a
chalky, drying mouth feel to the food that makes it organoleptically
unacceptable.

These
drawbacks
have been recently overcome by the addition of carboxymethylcellulose
to the a cellulose
prior to drying the final product. The addition of
carboxymethylcellulose
improves the functional properties so that the material can hydrate and
disperse with comparatively little mechanical effort. It also reduces
or
eliminates the chalky taste in many food formulations. This new
product, whose
trade name is Avicel RC, has substantially different properties from
the
original Avicel. Specifications and properties of Avicel RC are given
in Table
3. A great deal of the previous literature describing Avicel
applications is
not valid for Avicel RC. Therefore a clear cut distinction should be
made
between these two products in food applications and evaluations.

Food Applications

The main
food
applications for the original microcrystalline cellulose were described
by
Trauberman: (1) Avicel in dry form or as a gel can be incorporated as a
bulking
agent in many food products to effect significant calorie reduction
without
impairing the palatability or appearance of the food. (2) Avicel
dispersed in
water produces stable gels containing up to 20% or more of solids.
These gels
are spreadable, and at lower concentrations creamy colloidal
suspensions can be
obtained. (3) In dry form, Avicel is an effective absorbent and can
convert oil
base foods, such as cheese and peanut butter, and also syrups, such as
molasses
and honey, to free flowing, granular powders for use in dry package
mixes and
similar convenience foods.

The primary
application proposed for Avicel was as a new ingredient for the control
of
calories in a wide range of food products. The promotional literature
by the
manufacturer, Food Machinery Corp., proclaimed Avicel to be a
noncaloric
ingredient and stated that it contributes functional properties, such
as
stability, body bulk, opacity, texture, and palatability. These
applications
were disclosed and illustrated by Battista in a broad spectrum of
diversified
food uses. They were all basically reduced calorie food compositions.
The
examples covered are methods and formulations for making a wide variety
of low calorie
products, such as honey flavored doughnuts, peanut butter cookie dry
mix, bran
muffins, layer cake, fibrous breakfast food, chocolate pudding,
chocolate
dessert topping or sauce, soft pudding, peanut butter streusel type
crumb
topping, low calorie cream salad dressing, imitation butter or
margarine,
mayonnaise type salad dressing, cheddar cheese spreads, dry mix ice
cream,
malted milk shake, catsup, caramel candy, and milk chocolate.

Avicel RC
has
novel rheological properties, which makes it useful in the preparation
of
stable emulsions and suspensions such as pourable salad dressings and
chocolate
drinks. When properly dispersed, the particles of microcrystalline
cellulose
and carboxymethyl cellulose form a gel network of weakly bound
particles. This
gel structure stabilizes and prevents the coalescence of liquid
droplets of
emulsions as well as the settling out of solid particles in
suspensions. If a
shear force (such as shaking) is applied to this thixotropic system,
some of
the bonds break when the yield value is exceeded and the system flows.
Upon
standing, the gel structure gradually reforms to give the original
stable
emulsion or suspension. This property can be quite useful in the
formulation of
many food products.

Canned Shelf Stable Spreads and Salads

A fairly
recent
development has been the use of Avicel RC in the manufacture of canned
salad
and spread type products that are sterilized in the container. This
application
was made possible because of the ability of Avicel stabilized
emulsions, such
as salad dressings, to withstand sterilization conditions as severe as
240°F
for 75 minutes even in the presence of food acids. Discoloration was
not
experienced except where other heat sensitive substances were present.
These
salad dressings could be blended at any desired ratios with pieces of
chopped
meats or vegetables. It is now possible to retort in the container such
products as ham spread, chicken salad, tuna salad, salmon salad, potato
salad,
and macaroni salad. Durkee Famous Foods Co. has marketed a ready to
serve
canned tuna salad made with Avicel RC.

Salad Dressings

The use of
Avicel with water at solids levels of 30 36% gives gel like materials
varying
in degrees of thixotropy, viscosity, and opacity. These gels make it
possible
to prepare colloidal spreads containing up to 20% solids or more. These
colloidal gels are particularly useful in the formulation of smooth
food
products such as dressings, spreads, dips, sauces, and aerosol type
toppings.

At higher
solids
contents, the gels have the physical characteristics of animal fats or
hydrogenated vegetable oils. Vegetable oils and fats normally used in
products
similar to mayonnaise or salad dressing can be partially replaced with
Avicel, thus
reducing the caloric values by more than 50%. By combining the gels
with edible
oils or fats and using the proper dispersing agent, calorie control
foods that
taste like sour cream, hollandaise sauce, and cheese dips can easily be
made.

One
such product, a low calorie
salad topping containing 82 % fewer calories, has been marketed by Otto
Seidner, Inc., of Westerly, Rhode Island. This product, made with
Avicel,
contains only 3½ calories per teaspoon instead of the normal 20 per
teaspoon.

Frozen
Desserts

Frozen desserts with better
eating quality, added
heat shock stability and improved control of ice crystal formation have
been
claimed through the use of microcrystalline cellulose. The cellulose
particles,
a source of solids, are said to give body, bite resistance, and
chewiness to
frozen desserts. In addition, the added stiffness improves the
extrudibility of
the products. Avicel RC has been used in ice cream, sherbet, ice milk,
soft serve
ice cream, and artificially sweetened ice cream.

Aerosol Toppings

Aerosol
(foamable) preparations, such as toppings, possessing excellent body,
spreadability, and stability, are easily prepared using Avicel RC. The
value of
Avicel in aerosol or foamed food toppings has been illustrated in a
patent by
Herald. In addition to reduced caloric content, toppings made with
Avicel also
have the desirable properties of foam retention (no sagging),
smoothness in
appearance and eating quality, and a rich mouth feel despite the lower
content
of fatty materials. In addition, it was claimed that the products after
extrusion and foaming do not leak water, collapse, or develop a coarse
texture
on standing.

Dairy Type Products

Avicel RC
has
found application in the formulation of various synthetic or simulated
dairy
products. A synthetic product, Sour Kreme dressing, containing 40% less
calories than sour cream has been proposed for special dietary needs.

A
nondairy synthetic cream has
been prepared in the form of a stable, white emulsion resembling real
cream,
yet containing no dairy ingredients. In addition, coffee whiteners made
with
Avicel RC exhibit superior keeping qualities and an ability to
withstand
several freeze thaw cycles.

A
formulated
nondairy product, Cheez Spread, which also maintains its texture and
consistency through many freeze thaw cycles is made possible by the
functional
properties of Avicel RC.

Free Flowing Spreads

Microcrystalline
cellulose, which has a vast surface area because of the many fissures
and holes
in the submicroscopic surface area, is extremely absorbent,
particularly to
fatty materials. This function or property makes it possible to convert
oily or
syrupy products into dry, free flowing powders. It has been suggested
that
butter flavored mixes can be formulated that will produce smooth,
butter flavored,
bread spreads upon the addition of water and stirring. By use of other
flavors,
such as cheese and spices, other flavored spreads may also be prepared.

Meat Products

The oil
absorbent
characteristics of Avicel offer advantages for use in various meat
products.
When used on the surface of bacon, it was claimed to curb curling and
prevent
sticking of the slice strip during storage. When used as a coating on
each side
of hamburger patties, it was claimed to prevent loss, of some of the
juices and
to reduce shrinkage. A suggested use for the material is in meat
products, to
be added by housewives or institutional operators to ground meat in
preparing
meat loaf dishes, sauces, etc. It could also be used as a vehicle for
absorbing
oily seasonings or flavor components and for incorporating these
materials into
processed meats.

Color Fixative

Natural
dyes can
be absorbed by the microcrystalline cellulose aggregates. The latter
may then
be used to carry edible dyes into fat based products, such as butter or
margarine, without causing speckling or blooming in the product.
Trauberman
suggested that since many of the oil soluble dyes have been banned for
food
use, this application may be helpful for coloring fatty foods with
water soluble
nontoxic natural vegetable dyes.

Battista
accomplished this by binding suitable colors, lakes, pigments, etc.,
onto the
cellulose crystallite aggregates. These were then used to color various
foods,
particularly those that tolerate little or no water, such as hard
candies,
bakery icings, confectionery coatings, cake mixes, and beverage powders.

Bakery and Pasta Products

In dry
form,
Avicel powder, which resembles flour, can be easily incorporated into
foods by
blending or homogenization. In baked goods, it has been used for the
production
of low calorie cookies marketed by Weston Biscuit Company. The cookies,
sold as
Sweet 16 cookies, contain only 16 calories apiece and are fortified
with
vitamins.

A pasta of
Avicel in water can be extruded into ribbons and other shapes. In this
way low calorie
spaghetti, macaroni, and other products can be made.

Cloud Agent

It has been
suggested that Avicel can be used as a clouding or opacifying agent for
beverages at concentrations of less than 0.5%. This was tried by the
Nestle
Company in its Keen soft drink powder in order to impart cloudiness to
the
reconstituted beverage.

Protective Film

Avicel also
has
effective film forming properties. It therefore has been suggested for
use as a
water soluble, edible protective coating for foods and has been claimed
to be
particularly suitable for frozen foods such as vegetables, meats, ice
cream,
confections, butter, and cheese.

Synthetic Hydrocolloids

Within the
last
two or three decades, various synthetic and chemically modified
hydrocolloids
have been created and investigated. Some of these polymers have
replaced older
traditional natural gums in various food applications, and increasing
commercialization of improved synthetic gums will undoubtedly stimulate
competition between these and the natural gums.

There are
organic chemists who believe that the day will come when every natural
product
will be synthesized in the laboratory, and at the same time improved
functionally in such a way as to overcome inherent undesirable
properties. On
the other hand, there are those who believe that synthetic gums will
never
economically replace the cheaper natural gums such as starch ($0.10
0.15 per
pound), gum arabic ($0.35 per pound), and guar and locust bean gum
($0.45 per
pound), and that at best the semisynthetics (chemically modified
starches,
celluloses, etc.) will be the limit of practicality for the synthetic
chemist.
But in all cases, the economic incentive and specific quality will be
the
guiding force behind these decisions.

In the
synthetic
gum field at present, most research efforts seem to be directed toward
two
objectives: (1) synthesis and development of gums having properties
identical
to and superior to those of the well known natural gums, and (2)
synthesis and
development of gums having completely new and novel properties for
entirely new
and yet undefined applications.

Several
completely
synthetic gums have been developed which have already been used
successfully in
the food industry or which have the potential of finding food
applications in
the future. The main hurdle for employment in foods is the lack of Food
and
Drug Administration clearance, which is based on lengthy feeding
studies, some
of which are in progress. But in general, these hydrocolloids have been
reported to be nontoxic and must eventually be considered for food
applications.

Polyvinylpyrrolidone (PVP)

Background

Polyvinylpyrrolidone
is a comparative newcomer to the field of industrial water soluble
polymers. It
was developed by W. Reppe in Germany in the late 1930s and was first
used
during the Second World War as a blood plasma expander. After the war,
other
uses, primarily in nonfood fields, were developed, and in 1956, the
General
Aniline and Film Corporation began full scale production of this
material in
the United States.

Polyvinylpyrrolidone
is a polymeric N vinyllactam known chemically as poly 1 vinyl 2
pyrrolidone,
but more generally as PVP. Its chemical structure is shown in structure
I. It
is produced commercially by a purely synthetic route involving
acetylene,
formaldehyde, ammonia, and hydrogen as shown in Eq. (1).

Domestically
the
General Aniline and Film Corp. produces four different viscosity
grades, which
are offered in both powder form and aqueous solutions. These differ
primarily
in molecular weight, as in the tabulation.

In
addition,
special pharmaceutical grades of PVP are available under the trade name
Plasdone, and food additive grades are supplied as Polyclar.

At
present these materials range
in price from a low of about $1.25 per pound to $3.20 per pound for the
pharmaceutical injectable grade. It is felt that its physiological
inertness
and its protective colloid function remain to be exploited in the food
field,
and that only a fraction of the market potential for PVP has been
realized to date.
With the growth of markets and long range development of PVP, the price
may
eventually come down to the range of 60 70 cents per pound and offer
severe
competition to other water soluble gums in this price range.

Properties

Polyvinylpyrrolidone
is very versatile and offers various functional properties for a
multitude of
applications. It has a wide solubility and compatibility range. It is
an
excellent protective colloid and suspending agent and has very good
film forming
properties. It is also a good binder and stabilizing agent and has
desirable
adhesive properties. It is a complexing agent and can be used for
detoxification purposes.

The
commercial versatility of
PVP, which has led to the increasing use of this polymer in a wide
variety of
fields, is due primarily to the following outstanding properties: (1)
wide
solubility and compatibility range, (2) complexing and detoxifying
ability, (3)
physiological acceptability, (4) protective colloid action, (5) film
forming
ability, (6) adhesive qualities.

Solubility

Polyvinylpyrrolidine
is readily soluble in cold water and gives fairly viscous solutions
(Fig. 1).
With lower molecular weight material, concentrations as high as 60% can
be
dissolved in aqueous media. The viscosity of PVP is not affected by pH
over the
broad range of 0 10. Solutions of PVP also have a high tolerance for
many
inorganic salts, particularly the lower molecular weight types. PVP
solutions
are stable over long periods if they are protected from mold growth by
antimycotics such as sorbic acid.

In
comparison
with other commercially available water soluble gums, PVP has unusual
solubility in organic solvents. It is soluble in the lower alcohols,
glycols,
nitroparaffins, methylene dichloride, amines, and organic acids, and
when it is
anhydrous the solubility range is increased to include ketones, esters,
and
aromatic hydrocarbons.

The
complexing action of PVP is
demonstrated by its ability to form molecular adducts with other
substances. In
some cases, the result is a solubilizing action, as with iodine in other cases the result is
a precipitating
action, as with tannins in beverages.

Film Formation

One of the
most
unusual properties of PVP is in its film forming nature. PVP can be
cast from a
variety of solvents to give films that are clear, glossy, and hard at
low
humidities. They are very hygroscopic and exhibit excellent adhesion to
a wide
variety of surfaces, such as glass, metals, plastics, and human hair.
As with
most water soluble resins, PVP films are hygroscopic and the degree of
water
absorption is a function of relative humidity. Because of its unique
properties, PVP film has found widespread application in the cosmetic
field,
where it is used extensively in the formulation of various hair sprays
and hair
fixative preparations. In this field it has also been used in barrier
creams,
hand cleaners, hand lotions, dentifrices, and shaving preparations as
well as
in deodorant sprays and after shave lotions.

Insoluble
films
having the same stability, physiological compatibility, and other
properties of
soluble PVP can be made by reacting PVP with polymeric carboxylic acid
compounds.

Toxicology

The
physiological background of PVP has been well explored because of its
earlier
uses as a blood plasma extender, and a long history of use has shown it
to be
essentially a physiologically inert material. PVP is essentially
nontoxic when
given by oral administration, skin absorption, inhalation, or
intravenous or
intraperitoneal injection. It is not a primary irritant, skin fatiguing
material, or sensitizer and
it is
nonantigenic.

By
definition
the acute oral toxicity (LD0) is greater than 100 g per kilogram of
body
weight. Acute intravenous toxicity (LD50) is equal to 12 15 g per
kilogram of
body weight. Chronic oral toxicity was also investigated by feeding
rats and
dogs 1 10% PVP K 30 by weight of their total diet for up to 24 months.
No toxic
effects or significant pathological changes attributable to the PVP
were
observed.

Food Applications

In the food
industry, PVP has found an important application in beverage
manufacture as a
clarifying agent. It is known that PVP forms insoluble complexes with
certain
tannins. This property is applied to clarification and chill proofing
of
vegetable and fruit beverages, such as beer, whiskey, wine, vinegar,
and fruit
juices. Usually, taste and clarity are improved and other desirable
properties
are enhanced. The trade name for PVP offered for beverage uses is
Polyclar in
the United States. PVP has been approved for use as a clarifying agent
in
beverages under prescribed conditions by Food and Drug Administration.

Beer

The use of
PVP
as a selected precipitant for tannins in beer was discovered. In
efforts to
find a method of getting rid of the tannins in beer in order to extend
shelf
life, McFarlane et al. conducted a long search for these selective
precipitants. They found that PVP was the most effective and useful.
Chill haze
is generally regarded as being due to a proteintannin complex formed by
a slow
reaction between barley protein, b globulin, and a tannin of unknown
structure
but probably of high molecular weight. Proteolytic enzymes such as
papain, the
active ingredient of most chill proofing agents, break down and
solubilize the
protein of the protein tannin complex. The chill stability imparted to
the beer
by this process may be of a temporary nature, since upon storage for
long
periods the components of the protein tannin complex may recombine and
reform a
haze. On the other hand, PVP is concerned with a tannin rather than a
protein
component, and since PVP removes all the tannins it would appear that
selective
precipitation will result in a more permanent chill proofing of the
beer.
McFarlane et al. found that under certain specified conditions PVP
permanently
removed the chill haze material from beer without harming palate
fullness,
flavor, or head retention. They found the optimum requirement to be
about 1 lb
of PVP per 100 barrels but
this varied
for beers brewed under different conditions. Insufficient PVP failed to
give
adequate protection, whereas an excess caused the appearance of haze
during
pasteurization. However, a method was described whereby the optimum
amount of
PVP for a given beer could be easily determined before proceeding to
full scale
brewing trials. In addition, the use of PVP to remove these tannins
improved
taste and taste stability, foam retention, chill haze stability, and
filtration
ease, and gave cleaner worts from the cooler, cleaner, better tasting
storage
beer, shorter storage time, a saving on hops, and lower enzymatic chill
proof
requirements.

The optimum
amount of PVP used generally falls within the range of 120 200 parts
per
million, or about 3 5 lb of PVP per 100 barrels of beer but the optimum must be
determined
experimentally for a given brewery. The usual practice in breweries is
to boil
the malt cereals and hops with water for a specified period, after
which the
hot liquid, called hot wort, is strained free of hops. It is
recommended that
the PVP be added a few minutes before the end of the kettle boil. At
this
stage, the PVP content after filtration of the finished beer is
properly zero
(less than 1 ppm). A different mechanism for preventing chillhaze takes
advantage of the observation that a large excess of PVP (an extra 100
200 ppm)
forms a soluble complex with the critical materials.

The
preferred
PVPs for preventing chill hazes in beer are the ones with molecular
weights of
less than 30,000. They are used at a level of less than 2lb per 100
barrels.

Stone, in a
later patent, claimed that McFarlanes clarification procedure could be
improved
by using the low molecular weight PVP polymers ( K 15), or copolymers
of PVP with
olefinic compounds such as vinyl acetate or vinyl alcohol. These
additives
would stabilize the beer or ale without causing precipitation of the
protein tannin
complex.

Hoggan
reported
a unique advance in brewing technology involving the use of an
insoluble form
of PVP. This material (once known as AT 496, now called Polyclar AT),
is
reported to have the advantages of water soluble PVP, such as the high
selectivity for tannins (anthocyanogens), without the disadvantages
that may be
associated with the presence of residual PVP in the finished beer. In
addition,
it appears to possess a particular affinity for the part of the
anthocyanogens
that combine specifically with protein to form chill haze materials.
Other
advantages stated are that Polyclar AT did not absorb bittering
substances and
that there is no effect on the foam properties of treated beer. In
addition,
copper content is reduced significantly and the flavor is not adversely
affected. In fact, it was reported that beers treated with Polyclar AT
possess
less astringent after bitterness, which seems to help accentuate the
bitterness
associated with the isohumulones. The levels recommended are about 3 4
lb per
100 barrels.

Berntsson
showed
that the haze forming constituents in beverages are precipitated by the
use of
0 8 g PVP per hectoliter of beverage, with the preferred PVP having a
molecular
weight of 7,500 40,000.

General
developments in this field led to the production and sale of a
specialized PVP
product, Polyclar H, for use in the fining and stabilizing of beer
(General
Aniline and Film Corp., 1958). Polyclar H, currently sold by the
General
Aniline and Film Corporation for specific use as a clarifying and
stabilizing
agent for the brewing industry, is claimed to contribute the following
desirable
attributes: (1) markedly increases the amount of trub removed as hot
break (2) modifies
the characteristics of trub,
facilitating removal by decanting, filtering, or centrifuging (3) reduces potential haze
materials in the
beer (4)
significantly reduces the
amount of chill proof required (5)
enhances the flavor and foam properties of finished beer (6) improves the clarity and
stability of beer
(7) exerts a hop
sparing action (8)
improves stability to taste.

More recent
developments have led to the use of the insoluble, cross linked form of
PVP
(Polyclar AT) as a clarifying and stabilizing agent for beer and also
wine,
whiskey, fruit juices, and tea. Sucietto used a combination of cross
linked PVP
and activated charcoal to render aged distilled whiskeys haze resistant.

Post Reviews

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